UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Orientation of fishes to low frequency sound sources and the role of the lateral line system Russell, Ian John 1966

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1966_A6_7 R8.pdf [ 6.44MB ]
Metadata
JSON: 831-1.0104786.json
JSON-LD: 831-1.0104786-ld.json
RDF/XML (Pretty): 831-1.0104786-rdf.xml
RDF/JSON: 831-1.0104786-rdf.json
Turtle: 831-1.0104786-turtle.txt
N-Triples: 831-1.0104786-rdf-ntriples.txt
Original Record: 831-1.0104786-source.json
Full Text
831-1.0104786-fulltext.txt
Citation
831-1.0104786.ris

Full Text

THE ORIENTATION OF FISHES TO LOW FREQUENCY SOUND SOURCES AND THE ROLE OF THE LATERAL LINE SYSTEM, by IAN JOHN RUSSELL B.Sc. U n i v e r s i t y o f London A T h e s i s S u b m i t t e d i n P a r t i a l F u l f i l m e n t o f the Requirements f o r t h e Degree o f MASTER OF SCIENCE i n t h e Department o f ZOOLOGY We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA AUGUST, 1966 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study, I further agree that permission.for extensive copying of t h i s thesis f o r scholarly purposes may be granted by the Head of my Department or by his representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. The Uni v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada ( i ) ABSTRACT A t h e o r e t i c a l a n a l y s i s o f t h e a c o u s t i c f i e l d around a sound s o u r c e s u g g e s t e d t h a t f i s h would be a b l e to l o c a t e a sound s o u r c e by d e t e c t i n g t h e a s s o c i a t e d near f i e l d d i s p l a c e m e n t s w i t h t h e i r l a t e r a l l i n e system. B l i n d e d g o l d f i s h and Mexican b l i n d cave c h a r a c i n s were a b l e t o l o c a t e b o t h s t a t i o n a r y o b j e c t s and sound s o u r c e s . The l a t e r a l l i n e system was i m p l i c a t e d as the d i r e c t i o n a l l y s e n s i t i v e organs i n v o l v e d . B l i n d cave f i s h were a b l e t o l o c a t e b o t h s t a t i o n a r y o b j e c t s and a sound s o u r c e a g a i n s t a background n o i s e . The e x i s t e n c e o f a n o i s e s u p p r e s s i n g mechanism t o the l a t e r a l l i n e o rgans was s u g g e s t e d . An e f f e r e n t nervous s u p p l y was shown to i n n e r v a t e a n t e r i o r l a t e r a l l i n e organs o f g o l d f i s h , and t h e i n h i b i t o r y n a t u r e o f t h e e f f e r e n t n e r v e s was demonstrated. The e f f e r e n t n e r v e s were found t o be i n s e n s i t i v e t o t h e s t i m u l a t i o n o f a c o u s t i c a l l y s e n s i t i v e organs on the f i s h , but responded t o ch a n g i n g s t a t e s o f mu s c u l a r a c t i v i t y i n t h e f i s h . Swimming g o l d f i s h changed h y d r o d y n a m i c a l l y d u r i n g r e s p i r a t i o n from b l u f f b o d i e s , when t h e i r mouths were s h u t , t o s t r e a m l i n e d b o d i e s , when t h e i r mouths were open. T h i s change i n c o n f i g u r a t i o n l e a d t o t h e p r o p o s a l t h a t t h e a n t e r i o r l a t e r a l l i n e organs f u n c t i o n b oth as v e l o c i t y d e t e c t o r s and n e a r f i e l d d i s p l a c e m e n t d e t e c t o r s . ( i i ) A c e n t r a l l o c a t i o n was s u g g e s t e d f o r a neuro-p h y s i o l o g i c a l n o i s e a t t e n u a t i n g system t o t h e l a t e r a l l i n e system, and t h e e f f e r e n t n e r v e s i n n e r v a t i n g t h e l a t e r a l l i n e o rgans were s u g g e s t e d t o form p a r t o f a mechanism r e f l e x i v e l y c o n t r o l l i n g swimming v e l o c i t y . ( i i i ) TABLE OF CONTENTS Page ABSTRACT ( i ) TABLE OF CONTENTS ( i i i ) LIST OF TABLES (v) LIST OF ILLUSTRATIONS ( v i ) LIST OF GRAPHICAL FIGURES ( v i i i ) ACKNOWLEDGMENT ( i x ) GENERAL INTRODUCTION BEHAVIOUR:PART I 9 I n t r o d u c t i o n 9 E x p e r i m e n t a l 12 R e s u l t s 16 D i s c u s s i o n 25 BEHAVIOUR:PART 2 32 I n t r o d u c t i o n 32 E x p e r i m e n t a l 35 R e s u l t s 38 D i s c u s s i o n 44 ' NEUROPHYSIOLOGY:PART I 48 I n t r o d u c t i o n 48 E x p e r i m e n t a l 51 R e s u l t s 60 D i s c u s s i o n 72 NEUROPHYSIOLOGY:PART 2 77 I n t r o d u c t i o n 77 E x p e r i m e n t a l 79 R e s u l t s 80 D i s c u s s i o n 85 HYDRODYNAMIC INVESTIGATION 88 I n t r o d u c t i o n 88 E x p e r i m e n t a l 90 R e s u l t s 94 D i s c u s s i o n 97 GENERAL DISCUSSION SUMMARY REFERENCES ( i v ) Page 101 116 118 (v) LIST OF TABLES Page I The r e a c t i o n s e x h i b i t e d by b l i n d g o l d f i s h t o 17 the p r e s e n c e o f a v e r t i c a l r o d b l o c k i n g t h e i r p a t h s o f l o c o m o t i o n . I I The r e a c t i o n s e x h i b i t e d by b l i n d Mexican cave f i s h 18 t o t h e p r e s e n c e o f a v e r t i c a l r o d b l o c k i n g t h e i r p a t h s o f l o c o m o t i o n . I I I The r e a c t i o n s made by b l i n d e d g o l d f i s h when approach- 19 i n g a sound s o u r c e . IV The r e a c t i o n s o f Mexican b l i n d cave f i s h when 20 a p p r o a c h i n g a sound s o u r c e . V The c a l i b r a t i o n o f t h e p r e s s u r e changes g e n e r a t e d 40 i n t h e s m a l l tank by a background n o i s e f o r d i f f e r e n t f r e q u e n c i e s . VI The e f f e c t o f n o i s e o f c o n s t a n t a m p l i t u d e and 41 f r e q u e n c y on t h e a b i l i t y o f b l i n d cave f i s h t o d e t e c t a r o d p l a c e d i n t h e i r p a t h . V I I The e f f e c t o f n o i s e o f c o n s t a n t a m p l i t u d e and 42 f r e q u e n c y on t h e a b i l i t y o f b l i n d cave f i s h t o d e t e c t a v i b r a t i n g bead p l a c e d i n t h e i r p a t h . V I I I Impulses r e c o r d e d f rom t h e p r o x i m a l end o f a c u t ner v e o r i g i n a l l y i n n e r v a t i n g l a t e r a l l i n e o r g an n9. 61 IX Impulses r e c o r d e d from t h e i p s i l a t e r a l p r o x i m a l end 63 o f a c u t ne r v e s u p p l y i n g l a t e r a l l i n e organ n7, w i t h t h e c o n t r a l a t e r a l s i d e of t h e head s t i m u l a t e d w i t h v i b r a t i n g a i r b u b b l e s . X The e f f e c t o f an a p p l i c a t i o n o f s t r y c h n i n e t o t h e 67 l a t e r a l l i n e organs o f t h e n a s a l c a n a l upon t h e d i s c h a r g e of t h e f i b e r s f r om t h e b u c c a l branch o f th e f a c i a l n e r v e s u p p l y i n g t h e o r g a n s . XI The e f f e c t o f c u t t i n g n e r v e Z o f the b u c c a l b r a n c h of 68 the f a c i a l n e r v e , upon t h e d i s c h a r g e s r e c o r d e d i n th e d i s t a l p a r t of t h e f i b e r , and th e n a p p l y i n g s t r y c h n i n e l o c a l l y t o t h e organs i n n e r v a t e d by t h i s f i b e r i n the n a s a l c a n a l . X I I The a p p l i c a t i o n o f t u b e r c u r a r i n e c h l o r i d e i n t r a - 32 m u s c u l a r l y t o t h e o p e r c u l a r muscles o f g o l d f i s h , and th e changes i n e f f e r e n t a c t i v i t y a s s o c i a t e d w i t h t h e c h a n g i n g m u s c u l a r s t a t e of the f i s h when r e c o r d e d f r om n e r v e Z. ( v i ) LIST OF ILLUSTRATIONS. Page 1. A The r e l a t i o n s h i p between t h e a m p l i t u d e o f p u l s -a t i o n of a sphere and t h e d i s p l a c e m e n t of a p o i n t s i t u a t e d i n i t s n e a r f i e l d . B The r e l a t i o n s h i p between th e d i s p l a c e m e n t o f a sphere u n d e r g o i n g d i p o l a r o s c i l l a t i o n s , and t h e d i s p l a c e m e n t o f a p o i n t i n i t s n e a r f i e l d . C To i l l u s t r a t e a l e f t r i g h t c o n f u s i o n between two r e c e p t o r s i n t h e n e a r f i e l d o f a sound s o u r c e . D To i l l u s t r a t e a s e r v o s y s t e m c a p a b l e o f l o c a t i n g 3 a sound s o u r c e . 2. A A p e r s p e c t i v e view o f t h e s m a l l b e h a v i o u r tank and a p l a n view o f the p e r f o r a t e d p l a s t i c p l a t e i n w h i c h 3 mm. g l a s s r o d s were i n s e r t e d . B The v i b r a t i n g sound s o u r c e c o n s i s t i n g o f a g l a s 12 bead mounted on a t h i n r o d a t t a c h e d t o the m i c r o s t i r r e r d r i v e r u n i t . 3. A The bow wave s e t up ahead of a swimming Mexican b l i n d cave f i s h . B The i n t e r r u p t i o n o f t h e bow wave by t h e p r e s e n c e 28 of an o b j e c t i n t h e p a t h o f a b l i n d cave f i s h . 4. A A d i a g r a m of t h e arrangement of t h e a p p a r a t u s used i n the experiment t o measure the a c o u s t i c f i e l d o f t h e sound g e n e r a t e d i n t h e s m a l l tank by the e i g h t i n c h l o u d s p e a k e r . B The v i b r a t i o n a l movement of the base of t h e tank caused by t h e v i b r a t i o n s o f the diaphragm o f the l o u d s p e a k e r . C A q u a d r i p o l a r sound s o u r c e . 34 5. A The clamp used f o r h o l d i n g t h e f i s h r i g i d l y t h r o u g h -out t h e e x p e r i m e n t . B Schematic arrangement of t h e a p p a r a t u s used d u r i n g 52 t h e n e u r o p h y s i o l o g i c a l e x p e r i m e n t s . 6. Diagram o f t h e d i s s e c t e d ramus b u c c a l i s f a c i a l i s on 54 t h e r i g h t s i d e of t h e head of a g o l d f i s h . ( v i i ) Page 7. Schematic arrangement of e l e c t r o n i c r e c o r d i n g 56 a p p a r a t u s and s t i m u l a t i n g a p p a r a t u s used i n t h e n e u r o p h y s i o l o g i c a l e x p e r i m e n t s . 8. A B i p o l a r r e c o r d i n g s o f a c t i o n p o t e n t i a l s from a 61 f i n e b ranch of the ramus m a n d i b u l l a r i s V i n n e r v a t i n g t h e muscle a d d u c t o r mandibulae 3. B B i p o l a r r e c o r d i n g s o f a c t i o n p o t e n t i a l s from n e r v e Y o f the ramus b u c c a l i s f a c i a l i s . 9. S i m u l t a n e o u s r e c o r d i n g s of o p e r c u l a r movements and a c t i o n p o t e n t i a l s i n e f f e r e n t f i b e r s o f n e r v e Y. A F i s h out o f w a t e r . 81 B F i s h i n t h e w a t e r . 10. A Schematic d i a g r a m o f t h e o p t i c s o f t h e system used t o o b s e r v e b i r e f r i n g e n c e i n the H e c t o r b e n t o n i t e s o l u t i o n . B The arrangement o f the f l u i d p o l a r o s c o p e used 89 i n t h i s e x p e r i m e n t . C The arrangement of t h e o p t i c a l system used i n the e x p e r i m e n t . 11. Drawings made from photographs t a k e n o f f i s h swimming 95 t h r o u g h t h e H e c t o r b e n t o n i t e s o l u t i o n . 12. A model c o n s t r u c t e d t o show th e arrangement of t h e , 111 proposed n o i s e a t t e n u a t i n g mechanism a c t i n g upon second o r d e r l a t e r a l l i n e neurones i n t h e m e d u l l a o f a g o l d f i s h . ( v i i i ) L I ST OF GRAPHICAL FIGURES Page A The e f f e c t o f s t i m u l a t i n g t h e n a s a l l a t e r a l l i n e 61a c a n a l and r e c o r d i n g from t h e e f f e r e n t nerve s u p p l y i n g organ n9. B The e f f e c t o f s t i m u l a t i n g t h e s u b - o r b i t a l c a n a l 61a and r e c o r d i n g from t h e e f f e r e n t nerve s u p p l y i n g o r gan n9. C The e f f e c t o f s t i m u l a t i n g the t r u n k c a n a l and 61a r e c o r d i n g f rom t h e e f f e r e n t nerve s u p p l y i n g organ n9. D The e f f e c t o f s t i m u l a t i n g t h e hyomandibular c a n a l 61a and r e c o r d i n g f rom t h e e f f e r e n t nerve s u p p l y i n g o r gan n9. E,F,G,H,I and J The e f f e c t o f s t i m u l a t i n g t h e c o n t r a l a t e r a l s i d e 63a o f t h e head w i t h a i r b u b l e s and r e c o r d i n g from the i p s i l a t e r a l e f f e r e n t n e r v e s u p p l y i n g organ n7. K The e f f e c t o f an a p p l i c a t i o n o f s t r y c h n i n e t o t h e 67a l a t e r a l l i n e organs o f t h e n a s a l c a n a l upon t h e d i s c h a r g e o f t h e f i b e r s f r o m t h e b u c c a l b r a n c h o f t h e f a c i a l n e r v e s u p p l y i n g the o r g a n s . L The e f f e c t o f c u t t i n g n e r v e Z of t h e b u c c a l b r a n c h 69 o f t h e f a c i a l n e r v e upon t h e d i s c h a r g e s r e c o r d e d i n t h e d i s t a l p a r t o f t h e f i b e r , and th e n a p p l y i n g s t r y c h n i n e l o c a l l y t o the organs i n n e r v a t e d by t h i s f i b e r i n t h e n a s a l c a n a l . ' M The a p p l i c a t i o n o f t u b e r c u r a r i n e c h l o r i d e i n t r a - 82a m u s c u l a r l y t o t h e o p e r c u l a r muscles o f g o l d f i s h , and t h e changes i n e f f e r e n t a c t i v i t y a s s o c i a t e d w i t h t h e c h a n g i n g m u s c u l a r s t a t e of t h e f i s h when r e c o r d e d f r o m n e r v e Z. ACKNOWLEDGMENT The a u t h o r w i s h e s t o e x p r e s s h i s s i n c e r e thanks t o Dr. D. R a n d a l l f o r h i s g u i d a n c e , c o n s t r u c t i v e c r i t i c i s m and i d e a s on t h e p r o j e c t . Thanks a re due a l s o t o D r s . W.S. Hoar, P.A. D e h n e l , and H.D. F i s h e r f o r t h e i r h e l p f u l s u g g e s t i o n s t h r o u g h o u t t h e p r o j e c t and f o r r e a d i n g t h e t h e s i s d r a f t s . The a u t h o r i s i n d e b t e d t o Dr. B. Hughes o f t h e P a c i f i c N a v a l L a b o r a t o r y , E s q u i m a l t , f o r making a v a i l a b l e f a c i l i t i e s and g i v i n g h e l p and a d v i c e f o r t h e c a l i b r a t i o n o f a hydrophone. The photo e l a s t i c e x p e r i m e n t s were performed w i t h equipment k i n d l y l e n t by t h e Department o f M e c h a n i c a l E n g i n e e r i n g o f t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , and t e c h n i c a l a d v i c e and h e l p was g i v e n by Mr. G. Andrews o f the E n g i n e e r i n g Department t o whom the a u t h o r i s g r a t e f u l . The a u t h o r w i s h e s t o thank M i s s J a n i c e H a l l f o r t y p i n g t h e t h e s i s and Mrs. C a r l a Beaumont f o r h e l p w i t h t h e p r e p a r a t i o n o f t h e f i g u r e s . The a u t h o r was f i n a n c i a l l y s u p p o r t e d t h r o u g h o u t the p r o j e c t by a N;A.T.O. s t u d e n t s h i p awarded by t h e S c i e n t i f i c R e s e a r c h C o u n c i l o f G r e a t B r i t a i n . GENERAL INTRODUCTION F i s h a re s u p p l i e d w i t h two r e c e p t o r systems w h i c h a re thought t o respond t o a c o u s t i c phenomena. The f i r s t o f t h e s e systems a re t h e e a r s and t h e s e have been shown t o be p r e s s u r e r e c e p t o r s (Bekesy 1960). The second of t h e s e systems i s t h e l a t e r a l l i n e system o f r e c e p t o r s w h i c h are d i s p l a c e m e n t s e n s i t i v e ( H a r r i s G.G. and B e r g e i j k 1962) . I f a f i s h can l o c a l i s e a sound s o u r c e under w a t e r , then e i t h e r o f t h e s e systems might be o p e r a t i v e . The p r e s e n t r e s e a r c h programme i s o r i e n t a t e d towards d e t e r m i n i n g i f f i s h can l o c a l i s e a sound s o u r c e under w a t e r , whether t h e o r e t i c a l l y t h e l a t e r a l l i n e organs can be i m p l i c a t e d , and t h e r o l e t h a t e f f e r e n t n e r v e f i b e r s , t h a t p o s s i b l y i n n e r v a t e t h e l a t e r a l l i n e o r g a n s , p l a y i n c o d i n g i n f o r m a t i o n r e c e i v e d a t t h e l e v e l o f the r e c e p t o r . W i t h t h e s e g e n e r a l q u e s t i o n s i n mind t h e f o l l o w i n g s p e c i f i c q u e s t i o n s have been asked e x p e r i m e n t a l l y . a) Which, i f any, o f t h e two systems c o u l d be used by a f i s h t o l o c a l i s e a sound s o u r c e under w a t e r ? b) Are f i s h a b l e to l o c a l i s e a sound s o u r c e under w a t e r i n bo t h q u i e t and n o i s y c o n d i t i o n s ? c) I s t h e r e an e f f e r e n t nervous s u p p l y to t h e l a t e r a l l i n e and what r o l e , i f any, do t h e s e n e r v e s p l a y at t h e r e c e p t o r ? - 2 -d) Are t h e r e s p i r a t o r y movements p o s s i b l y used by a f i s h as an a i d t o l o c a l i s e a sound s o u r c e ? The n a t u r e of a sound s o u r c e and i t s a s s o c i a t e d a c o u s t i c phenomena s h o u l d be c o n s i d e r e d f i r s t . The s i m p l e s t sound s o u r c e i s a p u l s a t i n g sphere u n d e r g o i n g changes i n volume. As t h e sphere changes volume i t c o n c e n t r i c a l l y and u n i f o r m l y d i s p l a c e s w a t e r around i t s e l f . T h i s d i s p l a c e m e n t d e c r e a s e s i n a m p l i t u d e as the d i s t a n c e from t h e c e n t r e o f the sphere i n c r e a s e s because the w a t e r has t o be d i s p l a c e d o v e r a g r e a t e r s u r f a c e a r e a ( F i g u r e l a ) . The d i s p l a c e m e n t o f t h e wa t e r ( e q u a t i o n i ) at a d i s t a n c e r from t h e c e n t r e o f the sphere o f r a d i u s A i s p r o p o r t i o n a l t o t h e a m p l i t u d e o f t h e p u l s e D and t h e s u r f a c e a r e a o f t h e c o n c e n t r i c s phere o f r a d i u s r . I f w a t e r was i n c o m p r e s s i b l e t h i s n o n - p r o p a g a t i n g d i s p l a c e m e n t known as t h e ne a r f i e l d d i s p l a c e m e n t would be the o n l y a c o u s t i c phenomenum produced by a p u l s a t i n g s p h e r e . Water i s not i n c o m p r e s s i b l e and an e l a s t i c component, t h e p r e s s u r e wave, i s g e n e r a t e d . T h i s i s a pr o p a g a t e d wave and s a t i s f i e s t h e c o n d i t i o n s o f t h e normal wave e q u a t i o n w h i c h d e s c r i b e s how the a m p l i t u d e o f t h e wave i s d e c r e a s e d at a r a t e i n v e r s e l y p r o p o r t i o n a l t o the d i s t a n c e from the c e n t r e of t h e s p h e r e . I t f o l l o w s t h a t a t a c r i t i c a l d i s t a n c e R away from the c e n t r e o f a p u l s a t i n g s p h e r e , t h e d i s p l a c e m e n t - 3 -F i g u r e 1 A The r e l a t i o n s h i p between t h e a m p l i t u d e o f p u l s -a t i o n D o f a sphere r a d i u s A, and t h e d i s p l a c e m e n t d o f a p o i n t s i t u a t e d i n t h e n e a r f i e l d and a d i s t a n c e r away fr o m t h e c e n t r e o f t h e s p h e r e . B The r e l a t i o n s h i p between t h e d i s p l a c e m e n t A o f d sphere r a d i u s A u n d e r g o i n g d i p o l a r o s c i l l a t i o n s , and th e d i s p l a c e m e n t o f a p o i n t s i t u a t e d a d i s t a n c e r from t h e c e n t r e o f the s p h e r e , and a t an a n g l e 6 t o t h e p a t h o f i t s o s c i l l a t i o n . d r i s t h e r a d i a l component of d i s p l a c e m e n t . d0 i s t h e a n g u l a r component o f d i s p l a c e m e n t . C The i l l u s t r a t i o n o f a l e f t , r i g h t c o n f u s i o n between r e c e p t o r s AB and A B 1 where t h e same ti m e and a m p l i t u d e d i f f e r e n c e s e x i s t i n r e c e i v i n g p r e s s u r e waves from a p o i n t sound s o u r c e P. A t i m e and a m p l i t u d e d i f f e r e n c e can e x i s t i f r e c e p t o r s ABB 1 are moved t o p o s i t i o n R S S 1 where t h e time d i f f e r e n c e between AB i s g r e a t e r t h a n between RS, but t h e a m p l i t u d e d i f f e r e n c e between AB i s l e s s t h a n between RS. D T h i s i l l u s t r a t e s a s e r v o system c a p a b l e o f l o c a t i n g p o i n t P. A and B r e c e i v e t h e same time and p r e s s u r e d i f f e r e n c e s . AB i s then swung t h r o u g h a n g l e 0 t o AB3" and t h e v a l u e o f the e r r o r s i g n a l t h u s gener-a t e d i s p r o p o r t i o n a l t o Cos 6 and t h e s i g n and magni-tude o f t h e s i g n a l l o c a t e s P. - 4 -a m p l i t u d e w i l l be e q u a l t o t h e p r e s s u r e a m p l i t u d e . D i s t a n c e s l e s s t h a n R from t h e c e n t r e o f the sphere f a l l i n t o a zone known as t h e n e a r f i e l d . T h i s c o n s i s t s o f b o t h near f i e l d d i s p l a c e m e n t waves and p r o p a g a t e d p r e s s u r e waves. At d i s t a n c e s g r e a t e r t h a n R, a zone known as the f a r f i e l d e x i s t s . T h i s e s s e n t i a l l y c o n s i s t s f o r t h e most p a r t o f p r e s s u r e waves, because t h e d i s p l a c e m e n t e f f e c t r a p i d l y a t t e n u a t e s . The n e a r f i e l d d i s p l a c e m e n t i s a v e c t o r q u a n t i t y h a v i n g b o t h magnitude and d i r e c t i o n , as opposed t o t h e f a r f i e l d p r e s s u r e wave w h i c h has o n l y magnitude and no d i r e c t i o n . I n t h e s p e c i a l case o f t h e a c o u s t i c f i e l d a s s o c i a t e d w i t h a p u l s a t i n g s p h e r e , a s i n g l e d i s p l a c e m e n t d e t e c t o r s i t u a t e d i n the n e a r f i e l d would be a b l e t o l o c a l i s e t h e s o u r c e , whereas t h r e e p r e s s u r e r e c e p t o r s would be r e q u i r e d i n t h e f a r f i e l d . A s p here o s c i l l a t i n g a l o n g one a x i s i s t h e n e x t s i m p l e s o u r c e o f sound t o be c o n s i d e r e d . T h i s motion i s s i m i l a r t o t h e p r o p u l s i v e movements of f i s h e s and i n v e r t e b r a t e s and i s , t h e r e f o r e , one o f t h e most common s o u r c e s o f v i b r a t i o n s found i n the a q u a t i c environment. F i g u r e l b shows a sphere u n d e r g o i n g l i n e a r o s c i l l a t i o n s , p u s h i n g w a t e r ahead o f i t , and d r a w i n g w a t e r from b e h i n d . F i g u r e l b and e q u a t i o n s i i and i i i show t h a t th e d i s p l a c e m e n t o f w a t e r caused by t h i s motion can be a n a l y s e d - 5 -i n t o two components, a r a d i a l component and an a n g u l a r d i s p l a c e m e n t . P a r a l l e l t o t h e a x i s o f motion o n l y r a d i a l d i s p l a c e m e n t e x i s t s , and at 90° t o t h i s a x i s o n l y a n g u l a r d i s p l a c e m e n t e x i s t s . F o r t h i s model a s i n g l e d i s p l a c e m e n t d e t e c t o r p l a c e d i n t h e n e a r f i e l d c o u l d g i v e no i n f o r m a t i o n about t h e p o s i t i o n o f the sound s o u r c e because t h e m o t i o n has two components, and t h e a n g l e 0 would have to be known, and knowing t h i s would a l r e a d y presume knowledge o f t h e p o s i t i o n o f t h e s p h e r e . The a c o u s t i c p r o p e r t i e s o f the l a s t d e s c r i b e d sound s o u r c e r e q u i r e t h a t at l e a s t two r e c e p t o r s , whether p r e s s u r e r e c e p t o r s o r d i s p l a c e m e n t r e c e p t o r s , are needed t o l o c a l i s e the sound s o u r c e , p r o v i d i n g t h e sound s o u r c e and r e c e p t o r s are a l l i n t h e same p l a n e . I f two d i s p l a c e m e n t o r p r e s s u r e r e c e p t o r s A and B are p l a c e d i n t h e f i e l d o f sound s o u r c e P as shown ( F i g u r e l c ) t h e n B w i l l r e c e i v e the p r e s s u r e wave e a r l i e r and w i t h a g r e a t e r a m p l i t u d e t h a n A. However, t h i s c o n f i g u r a t i o n can l e a d t o a l e f t - r i g h t c o n f u s i o n i f B i s moved t o B f where the same a m p l i t u d e and t i m e d i f f e r e n c e s e x i s t between A and B* as d i d between A and B. A t i m e and a m p l i t u d e c o n f u s i o n can a l s o e x i s t w i t h t h i s c o n f i g u r a t i o n i f ABB' i s moved c l o s e r to t h e sound s o u r c e P t o a new p o s i t i o n RSS*. I n t h i s new p o s i t i o n the time d i f f e r e n c e between A and B i s g r e a t e r than between R and S, but t h e a m p l i t u d e d i f f e r e n c e i s f a r l e s s between A and B than between R and S. - 6 -B e r g e i j k (1963) who f i r s t d e s c r i b e d t h e two t y p e s o f c o n f u s i o n s u g g e s t e d e m p l o y i n g one of two methods t o overcome t h i s c o n f u s i o n . One s o l u t i o n was t o i n c l u d e an e x t r a p r e s s u r e r e c e p t o r g i v i n g a minimum o f t h r e e r e c e p t o r s , and t h e o t h e r was t o i n c l u d e the two r e c e p t o r s i n a s e r v o system. The s e r v o system would o r i e n t a t e A and B i n such a manner t h a t t h e y would b o t h r e c e i v e the same a m p l i t u d e p r e s s u r e wave at t h e same time ( F i g u r e I d ) . However, t h i s would i n t r o d u c e a n o t h e r c o n f u s i o n , a f r o n t - b a c k c o n f u s i o n , w h i c h c o u l d be overcome by d e l i b e r a t e l y s w i n g i n g B t h r o u g h a known a n g l e 0 t o a new p o s i t i o n B*. T h i s d e f l e c t i o n would g e n e r a t e an e r r o r s i g n a l i n t h e s e r v o system, t h e magnitude and s i g n o f w h i c h would the n d e t e r m i n e t h e p o s i t i o n o f P. I n t h i s case t h e magnitude of the e r r o r s i g n a l would be p r o p o r t i o n a l t o Cos 0 w h i c h changes v e r y s l o w l y f o r s m a l l a n g l e s . A more s e n s i t i v e c o n f i g u r a t i o n i s r e p r e s e n t e d by RSS' i n f i g u r e I d . I n t h i s c a s e the e r r o r s i g n a l i s p r o p o r t i o n a l to s i n e 0 w h i c h changes r a p i d l y f o r s m a l l a n g l e s . I t i s c o n c l u d e d , from a t h e o r e t i c a l p o i n t o f v i e w , t h a t a maximum of t h r e e r e c e p t o r s , o r two r e c e p t o r s and a s e r v o system, i s r e q u i r e d t o d e t e c t a sound s o u r c e under w a t e r e x c e p t f o r t h e s p e c i a l case where the sound s o u r c e i s a p u l s a t i n g s p h e r e . Under t h i s c o n d i t i o n o n l y one d i s -placement r e c e p t o r need be r e q u i r e d . - 7 -A l t h o u g h t h e e a r s o f v e r t e b r a t e s are g e n e r a l l y c o n s i d e r e d to be p r e s s u r e r e c e p t o r s , the i n n e r e a r has been shown t o be d i s p l a c e m e n t s e n s i t i v e (Bekesy 1960), and t h e m i d d l e e a r s e r v e s the purpose o f t r a n s d u c i n g p r e s s u r e waves i n t o d i s p l a c e m e n t waves. The m i d d l e e a r o f f i s h e s i s c o n s i d e r e d t o be t h e swim b l a d d e r , a gas b u b b l e w h i c h , by o b e y i n g B o y l e s Law, changes volume i n r e s p o n s e to s u r r o u n d i n g p r e s s u r e f l u c t u a t i o n s . The volume changes are t r a n s l a t e d i n t o d i s p l a c e m e n t s o f t h e w a l l s o f t h e swim b l a d d e r w h i c h are conducted d i r e c t l y t o t h e i n n e r e a r , as f o r example i n the C l u p e i d s , o r i n d i r e c t l y by t h e Weberian O s s i c l e s , as i n the O s t e r i p h y s i . Thus, f i s h p o s s e s s two i n n e r e a r s but o n l y one p r e s s u r e s e n s i t i v e m i d d l e e a r . T h e r e f o r e , on t h e o r e t i c a l grounds, t h e e a r s of f i s h e s are p r e c l u d e d f r o m b e i n g c o n s i d e r e d d i r e c t i o n a l l y s e n s i t i v e t o sound s o u r c e s by v i r t u e t h a t t h e y p o s s e s s i n e f f e c t o n l y one p r e s s u r e s e n s i t i v e t r a n s d u c e r between them. L a t e r a l l i n e organs more th a n s a t i s f y the two minimum c o n d i t i o n s f o r a d i r e c t i o n a l l y s e n s i t i v e , a c o u s t i c a l l y s e n s i t i v e system. F i r s t l y , t h e y are d i s p l a c e m e n t r e c e p t o r s , so t h a t i n t h e s p e c i a l c o n d i t i o n o f a sound s o u r c e c o n s i s t i n g o f a p u l s a t i n g s p h e r e , a f i s h w i t h a s i n g l e l a t e r a l l i n e organ c o u l d l o c a l i s e i t i f i t was i n t h e n e a r f i e l d o f t h e s p h e r e . S e c o n d l y , f i s h p o s s e s s many of t h e s e organs d i s t r i b u t e d o v e r t h e i r b o d i e s t h e r e b y s a t i s f y i n g t h e c o n d i t i o n t h a t f i s h r e q u i r e t h r e e r e c e p t o r s o c c u p y i n g d i f f e r e n t p o s i t i o n s - 8 -i n space t o l o c a l i s e a sound s o u r c e . Touch r e c e p t o r s a l s o f u l f i l t h e c r i t e r i a r e q u i r e d o f a system c a p a b l e o f d i r e c t i o n a l l y l o c a l i s i n g a sound s o u r c e . However, i t i s b e l i e v e d t h a t t h e i r s e n s i t i v i t y t o w a t e r d i s p l a c e m e n t i s l e s s than t h a t o f t h e l a t e r a l l i n e o rgans ( A d r i a n 1929) and t h e r e f o r e t h e f i e l d o f s e n s i t i v i t y o f t h e t o u c h r e c e p t o r s would be o v e r l a p p e d by the f i e l d o f the l a t e r a l l i n e o r g a n s . I n t h e e x p e r i m e n t s w h i c h f o l l o w , an i n v e s t i g a t i o n was made t o see i f f i s h have th e a b i l i t y t o l o c a l i s e a sound s o u r c e , and w h i c h o r g a n s , i f any, can be i m p l i c a t e d as t h o s e r e s p o n d i n g d i r e c t i o n a l l y . - 9 -BEHAVIOUR : PART I Are f i s h a b l e t o l o c a t e s t a t i o n a r y o b j e c t s and low f r e q u e n c y sound s o u r c e s by r e s p o n d i n g t o s t i m u l i o t h e r t h a n v i s u a l s t i m u l a t i o n . INTRODUCTION There i s an apparent p a u c i t y i n t h e f i e l d o f marine b i o - a c o u s t i c s o f i n f o r m a t i o n r e g a r d i n g t h e a b i l i t y o f f i s h t o l o c a t e low f r e q u e n c y sound s o u r c e s under w a t e r . T h i s p a u c i t y may, p a r t l y be a r e s u l t o f a g e n e r a l a c c e p t a n c e , by w o r k e r s i n the f i e l d o f marine b i o - a c o u s t i c s , o f the c o n c l u s i o n s drawn by t h e Germans Von F r i s c h and D i j k g r a a f (1935) and R h e i n h a r d t (1935), from t h e i r e x p e r i -ments t h a t f i s h do n o t o r i e n t a t e t o under w a t e r sound s o u r c e s . R e c e n t l y B e r g e i j k (1964) c r i t i c i z e d t h e e v i d e n c e p r e s e n t e d by t h e s e w o r k e r s on t h e grounds t h a t no a n a l y s i s of the s t i m u l u s f i e l d t o w h i c h the f i s h were s u b j e c t e d , o r t h e s e n s o r y a p p a r a t u s w i t h w h i c h t h e f i s h were r e s p o n d i n g , was g i v e n . B e r g e i j k deduced from t h e e v i d e n c e p r e s e n t e d i n Von F r i s c h and D i j k g r a a f * s e x p e r i m e n t s t h a t t h e f i s h were l o c a t e d f o r t h e most p a r t i n t h e f a r f i e l d o f the sound s o u r c e s used i n t h e i r e x p e r i m e n t s , and t h i s may be a r e a s o n why no r e s p o n s e s were g e n e r a l l y e l i c i t e d from t h e f i s h . However, Von F r i s c h and D i j k g r a a f d i d make t h e o b s e r v a t i o n t h a t f i s h used i n t h e e x p e r i m e n t s o r i e n t a t e d t hemselves w i t h r e s p e c t t o t h e sound s o u r c e when a h i g h i n t e n s i t y sound was used, and t h e f i s h were i n c l o s e p r o x i m i t y (10 - 20 cm) of the sound s o u r c e . T h i s e v i d e n c e i n d i c a t e s t h a t t h e f i s h - 10 -may have been o r i e n t a t e d t o t h e near f i e l d of t h e sound s o u r c e . K l e e r e k o p e r and Chagnon (1954), t h e o n l y o t h e r i n v e s t i g a t o r s , p r i o r t o 1964, t o s t u d y t h e d i r e c t i o n a l b e h a v i o u r o f f i s h i n t h e v i c i n i t y o f a sound s o u r c e , c o n c l u d e d t h a t f i s h a r e a b l e t o o r i e n t a t e t o sound s o u r c e s . U n f o r t u n a t e -l y t h e y gave no i n f o r m a t i o n on the n a t u r e of t h e a c o u s t i c f i e l d t o w h i c h t h e f i s h were s u b j e c t e d and thus t h e i r e v i d e n c e i s d i f f i c u l t t o i n t e r p r e t i n t h e l i g h t of r e c e n t knowledge. A major d i f f i c u l t y i n t h i s f i e l d o f b e h a v i o u r s t u d y i s f o r m u l a t i n g t h e c r i t e r i a by w h i c h a f i s h can be s a i d t o be l o c a t i n g o r f a i l i n g t o l o c a t e a sound s o u r c e . A l l o f t h e workers engaged i n t h i s f i e l d o f s t u d y p r i o r t o 1964 used t h e p r i n c i p a l o f t h e c o n d i t i o n e d r e f l e x i n a t t e m p t i n g t o a s c e r t a i n whether o r not t h e f i s h were o r i e n t a t i n g towards t h e sound s o u r c e . O b s e r v a t i o n s were made on the head movements o f t h e e x p e r i m e n t a l f i s h t o d i s c o v e r i f t h e y moved away from o r towards t h e sound s o u r c e depending upon t h e p r e - c o n d i t i o n i n g s t i m u l u s g i v e n t o t h e f i s h . T h i s c r i t e r i u m was c o n s i d e r e d u n s a t i s f a c t o r y because judgements were made on i l l d e f i n e d r e a c t i o n s o f t h e f i s h . The f i s h was not ob s e r v e d t o c o n t i n u e i t s i n i t i a l head movements i n t o an e f f o r t t o escape from the f i e l d o f the sound s o u r c e , o r to approach the sound s o u r c e . T h i s c r i t i c i s m i s i n p a r t i c u l a r l e v e l l e d a t t h e work of K l e e r e k o p e r and Chagnon. - 11 -The b e h a v i o u r e x p e r i m e n t s i n t h i s i n v e s t i g a t i o n have p u r p o s e f u l l y been performed w i t h u n c o n d i t i o n e d f i s h , and t h e e x p e r i m e n t s have been d e s i g n e d t o e l i c i t a c l e a r l y d e f i n e d r e s p o n s e from t h e f i s h when t h e y were p r e s e n t e d w i t h t h e e x p e r i m e n t a l s i t u a t i o n . The need t o d e f i n e t h e n a t u r e o f t h e sound s o u r c e used i n t h e s e e x p e r i m e n t s , and t o a n a l y s e the a c o u s t i c f i e l d s u r r o u n d i n g the sound s o u r c e was a p p r e c i a t e d , and f o r t h i s r e a s o n c a l c u l a t i o n s o f t h e d i s p l a c e m e n t e f f e c t o f t h e n e a r f i e l d have been g i v e n f o r v a r i o u s p o i n t s i n the near f i e l d o f t h e s t i m u l u s . - 12 -gure 2 A p e r s p e c t i v e view o f t h e s m a l l b e h a v i o u r t a n k , and a p l a n view o f t h e p e r f o r a t e d p l a s t i c p l a t e i n w h i c h t h e 3 mm. g l a s s r o d s were i n s e r t e d . The v i b r a t i n g sound s o u r c e c o n s i s t i n g of a g l a s s bead mounted on a t h i n r o d a t t a c h e d t o t h e m i c r o s t i r r e r d r i v e r u n i t . 0.3 CM DIAMETER 5 CM. 24 CM. MICROMANIPULATOR 25 CM. ARM, 2.5 5 CM. CM. 7 CM. E 20 CM. SOLENOID CLAMP GLASS ROD GLASS SPHERE B - 13 -EXPERIMENTAL I n the f i r s t p a r t o f t h e experiment e i g h t g o l d f i s h ( C a r a s s i u s a u r a t u s ) a p p r o x i m a t e l y 6 cm. l o n g were used. They a l l appeared h e a l t h y , and t h e s c a l e s c o v e r i n g t h e i r b o d i e s were complete and undamaged. Twenty hours b e f o r e t h e s t a r t o f t h e e x p e r i m e n t s f o u r o f t h e g o l d f i s h were s e l e c t e d from t h e h o l d i n g t a n k , w h i c h c o n t a i n e d w a t e r at 12°C, and were b l i n d e d by c a u t e r i z a t i o n . These f i s h were th e n r e t u r n e d t o t h e h o l d i n g t a n k . I n t h e second p a r t o f the experiment t h r e e b l i n d M e x ican Cave c h a r a c i n s ( A n o p t i c h t h y s sp.) were m a i n t a i n e d , f o r s e v e r a l days p r i o r t o t h e e x p e r i m e n t , i n a s m a l l aquarium c o n t a i n i n g w a t e r at 22°C. Two b e h a v i o u r t a n k s were used i n t h e s e e x p e r i m e n t s , and b o t h were c o n s t r u c t e d o f a s t e e l frame w i t h g l a s s s i d e s and base. One tank measured 30 x 30 x 60 cm. and t h e o t h e r measured 24 x 24 x 24 cm. A p l a s t i c p l a t e w i t h v e r t i c a l l y mounted g l a s s r o d s ( F i g u r e 2a) was p l a c e d i n t h e s m a l l e r o f t h e two t a n k s . Ten g l a s s r o d s 7 mm. i n d i a m e t e r and 40 cm. l o n g were suspended v e r t i c a l l y , i n two rows p l a c e d 10 cm. a p a r t w i t h 10 cm. between each r o d , i n t h e l a r g e tank so t h a t one end of t h e r o d s r e s t e d on the bottom o f t h e t a n k . A sound s o u r c e was used at one s t a g e o f the e x p e r i m e n t . The s o u r c e was a g l a s s bead 1.5 mm. i n d i a m e t e r formed at one end o f a f i n e g l a s s r o d , the o t h e r end o f whic h was a t t a c h e d t o t h e d r i v e r u n i t o f a m i c r o s t i r r e r . A S i n e wave g e n e r a t o r connected t o t h e mi c r o s t i r r e r caused t h e g l a s s r o d and hence the g l a s s bead t o o s c i l l a t e back and f o r t h . U n f o r t u n a t e l y o n l y two f r e q u e n c i e s caused pure s i n u s o i d a l o s c i l l a t i o n s o f t h e g l a s s bead. These were 30 cps and 100 c p s . The d r i v e r u n i t was mounted on the arm o f a mi c r o m a n i p u l a t o r so t h a t t h e r o d hung v e r t i c a l l y downwards, and t h e bead c o u l d d e s c r i b e movements a l o n g 1 a x i s i n t h e h o r i z o n t a l p l a n e ( F i g u r e 2 b ) . F o r t h e f i r s t p a r t o f t h e experiment a l l o f the f i s h , t he e i g h t g o l d f i s h and t h e t h r e e b l i n d cave f i s h , were s u b j e c t e d t o t h e f o l l o w i n g t e s t : -A f i s h was removed from i t s h o l d i n g tank and p l a c e d i n a b e h a v i o u r tank ( t h e l a r g e tank f o r g o l d f i s h , and the s m a l l tank i n t h e case o f b l i n d cave f i s h ) w h i c h c o n t a i n e d w a t e r a t t h e same t e m p e r a t u r e as t h e w a t e r i n t h e h o l d i n g t a n k . The r e l e a s e o f t h e f i s h i n t o t h e b e h a v i o u r tank s i g n a l l e d t h e s t a r t o f t h e t e s t and t h e b e h a v i o u r o f t h e f i s h was ob s e r v e d as i t approached t h e r o d s . An approach t o a r o d was c o n s i d e r e d t o be made by t h e f i s h when i t swam i n s uch a d i r e c t i o n t h a t t h e r o d l a y d i r e c t l y i n i t s p a t h . An a v o i d a n c e r e a c t i o n was c o n s i d e r e d t o have been made when the f i s h a v o i d e d h i t t i n g t he r o d by t u r n i n g away from t h e r o d when i n c l o s e p r o x i m i t y t o i t . A d i s t a n c e o f 2-5 mm i n t h e case o f b l i n d cave f i s h . - 15 -T h i s t e s t was a p p l i e d t o each f i s h u n t i l the f i s h had approached a r o d t e n t i m e s , and t h e r e s u l t s o f o b s e r v a t i o n s were r e c o r d e d i n t a b u l a r form. In the second p a r t of t h e e x p e r i m e n t , u s i n g t h e above c r i t e r i a , t h e a b i l i t y o f the f i s h t o a v o i d a v i b r a t i n g g l a s s r o d was t e s t e d . The g l a s s r o d s w h i c h were suspended i n t h e b e h a v i o u r t a n k s were removed, and a f i s h , t a k e n from i t s h o l d i n g t a n k , was p l a c e d i n t h e a p p r o p r i a t e b e h a v i o u r t a n k . The sound s o u r c e d r i v e r u n i t was mounted on t h e arm o f t h e m i c r o - m a n i p u l a t o r above the s u r f a c e o f t h e w a t e r i n the tank so t h a t t h e f i n e g l a s s r o d a t t a c h e d t o the d r i v e r u n i t was suspended v e r t i c a l l y i n t h e w a t e r w i t h the g l a s s bead a few c e n t i m e t e r s above the bottom o f the t a n k . The r o d and bead were th e n moved about s l o w l y u n t i l t h e y l a y i n the p a t h o f the swimming f i s h , and t h e d r i v e r t u n i t was s w i t c h e d on c a u s i n g t h e bead t o v i b r a t e . The r e a c t i o n s o f t h e f i s h , when c o n f r o n t e d w i t h t h e v i b r a t i n g bead i n t h i s manner, were c l o s e l y examined, and the o b s e r v a t i o n s were t a b u l a t e d . T h i s t e s t was a p p l i e d t e n t i m e s t o each f i s h . At t h e end of t h e s e e x p e r i m e n t s the d i m e n s i o n s and a m p l i t u d e o f v i b r a t i o n of the g l a s s bead i n t h e tank were r e c o r d e d . - 16 -RESULTS The R e a c t i o n s E x h i b i t e d by G o l d f i s h when A p p r o a c h i n g a  S t a t i o n a r y V e r t i c a l Rod. B l i n d g o l d f i s h made avo i d a n c e r e a c t i o n s o n l y s i x t i m e s o ut o f 40 t r i a l s , when making approaches t o v e r t i c a l r o d s w h i c h were o b s t r u c t i n g t h e i r p a t h s o f l o c o m o t i o n . I t was thought p o s s i b l e t h a t g o l d f i s h b e h a v i o u r a l l y d i d not r e c o g n i z e t h e s i g n i f i c a n c e o f a r o d o b s t r u c t i n g t h e i r p a t h s , and t h u s might not make av o i d a n c e r e a c t i o n s even w i t h t h e i r e y e s i g h t i n t a c t . T h i s h y p o t h e s i s p r o v e d t o be i n c o r r e c t because none o f t h e unoperated g o l d f i s h f a i l e d t o a v o i d r o d s o b s t r u c t i n g t h e i r p a t h s a f t e r a t o t a l o f 40 t r i a l s ( T a b l e I ) . The R e a c t i o n s E x h i b i t e d by Mexican B l i n d Cave F i s h t o t h e Pr e s e n c e o f a S t a t i o n a r y V e r t i c a l Rod b l o c k i n g t h e i r P a t h s  o f L o c o m o t i o n . The r e s u l t s o f t h i s s e r i e s o f t e s t s ( T a b l e I I ) c l e a r l y i n d i c a t e t h e a b i l i t y o f the b l i n d cave f i s h t o make a v o i d i n g r e a c t i o n s when t h e i r p a t h s a re o b s t r u c t e d by g l a s s r o d s . A s e r i e s o f measurements p r e s e n t e d w i t h t h e s e d a t a i n d i c a t e t h e mean d i s t a n c e s away from t h e ro d s when the f i s h f i r s t s t a r t e d t o make an avo i d a n c e r e a c t i o n . - 17 -TABLE I The r e a c t i o n s e x h i b i t e d t o b l i n d g o l d f i s h t o t h e p r e s e n c e of a v e r t i c a l r o d b l o c k i n g t h e i r p a t h s o f l o c o m o t i o n . S t a t e o f V i s i o n I d e n t i f i c a t i o n o f G o l d f i s h No. o f Approaches No. o f A v o i d a n c e s B l i n d A 10 2 B l i n d B 10 0 B l i n d C 10 2 B l i n d D 10 2 Normal E 10 10 Normal F 10 10 Normal G 10 10 Normal H 10 10 D i a m e t e r o f Rod 0.7 cms. Temperature o f w a t e r 12°C +• 1°C. - 18 -TABLE I I The r e a c t i o n s e x h i b i t e d by b l i n d Mexican cave f i s h t o the pr e s e n c e o f a v e r t i c a l r o d b l o c k i n g t h e i r p a t h s o f l o c o m o t i o n . I d e n t i f i c a t i o n No. o f No. o f Mean D i s t a n c e o f Cave F i s h Approaches A v o i d a n c e s from S.S. 1 10 10 0.3 cms.+0.1 cms. 2 10 10 0.3 cms.+0.1 cms. 3 10 10 0.3 cms.+0.1 cms. Diameter o f Rod 0.3 cms. Temperature o f w a t e r 22°C. - 19 -TABLE The r e a c t i o n s made by b l i n d e d g o l d f i s h when a p p r o a c h i n g a sound s o u r c e . I d e n t i -f i c a t i o n o f G o l d f i s h Frequency o f Sound Source No. o f Approaches No. o f A v o i d -ances D i s t a n c e f r o m Sound A 100 c p s . 10 0 0 B 100 c p s . 10 0 0 C 100 c p s . 10 0 0 D 100 c p s . 10 0 0 A 30 c p s . 10 9 0.6 cm. B 30 c p s . 10 8 0.8 cm. C 30 c p s . 10 10 0.8 cm. D 30 c p s . 10 9 0.8 cm. 4- 0.2 cms. i - 20 -TABLE IV The r e a c t i o n s o f Mexican b l i n d cave f i s h when a p p r o a c h i n g a sound s o u r c e . I d e n t i -f i c a t i o n o f Cave F i s h Frequency o f -Sound Source No. o f Approaches No. o f A v o i d -ances D i s t a n c e f r om Sound 1 100 c p s . 10 10 4.5 cm. 2 100 c p s . 10 10 4.5 cm. 3 100 c p s . 10 10 4.5 cm. 1 30 c p s . 10 10 4.5 cm. 2 30 c p s . 10 10 4.5 cm. 3 30 c p s . 10 10 4.5 cm. + 0.1 cm. D i a m e t e r o f g l a s s bead = 0.15 cms. A m p l i t u d e o f v i b r a t i o n a t 100 c p s . =0.4 cms. A m p l i t u d e o f v i b r a t i o n at 30 c p s . a f t e r adjustment = 0.4 cms. - 21 -The R e a c t i o n s made by B l i n d e d G o l d f i s h when A p p r o a c h i n g a  Sound Source. The o s c i l l a t i o n s of t h e g l a s s bead c o n s t i t u t e s an approximate d i p o l a r s o u r c e o f v i b r a t i o n . T h i s means the a c o u s t i c f i e l d around the v i b r a t i n g sphere i s not u n i f o r m but t h e w a t e r d i s p l a c e m e n t i s maximum a l o n g the a x i s o f v i b r a t i o n , and minimum a t r i g h t a n g l e s t o t h i s a x i s . F o r t h i s r e a s o n the sphere was always s e t i n the p a t h s o f swimming f i s h so t h a t t h e a x i s o f v i b r a t i o n was a p p r o x i m a t e l y p a r a l l e l t o t h e swimming p a t h o f the f i s h . The d a t a p r e s e n t e d i n T a b l e I I i n d i c a t e s t h a t none of t h e f i s h made an av o i d a n c e r e a c t i o n t o t h e v i b r a t i n g bead when i t v i b r a t e d at 100 c p s . , but a v o i d e d i t when i t o s c i l l a t e d at 30 c p s . I n c l u d e d w i t h the d a t a a re measurements i n d i c a t i n g t h e mean d i s t a n c e away from t h e s o u r c e when each f i s h took a v o i d i n g a c t i o n . The R e a c t i o n s made by Mexican B l i n d Cave F i s h when A p p r o a c h i n g  a Sound Source. The cave f i s h were a b l e t o l o c a t e t h e p o s i t i o n of the v i b r a t i n g bead at both 100 c p s . and 30 c p s . They s t a r t e d t o make t h e i r a v o i d a n c e r e a c t i o n s a t a d i s t a n c e o f a p p r o x i m a t e l y 4.5 cms. from t h e g l a s s bead at b o t h f r e q u e n c i e s , w h i c h s u g g e s t e d t h a t t h e i r s e n s i t i v i t y t o t h e a c o u s t i c f i e l d o f t h e v i b r a t i n g r o d , between 30 and 100 c y c l e s p e r second ( T a b l e I V ) , was independent o f f r e q u e n c y , - 22 -At t h e t e r m i n a t i o n o f t h e s e t e s t s t h e a m p l i t u d e o f v i b r a t i o n of t h e r o d was measured v i s u a l l y , and t h e d i m e n s i o n s o f t h e g l a s s bead t a k e n ( T a b l e IV). - 23 -The D i s p l a c e m e n t o f Water R e q u i r e d t o E l i c i t a Response  i n G o l d f i s h and B l i n d Cave F i s h t o a 30 c p s . and 100 c p s .  D i p o l e Sound S o u r c e . A c c o r d i n g t o the r e s u l t s r e c o r d e d i n T a b l e I I I g o l d f i s h f i r s t responded t o t h e sound s o u r c e at d i s t a n c e s w h i c h v a r i e d between 0.5 cms. and 0.8 cms. from t h e g l a s s bead. The d i s p l a c e m e n t s at t h e s e p o i n t s may be c a l c u l a t e d u s i n g t h e r e l a t i o n s h i p g i v e n by H a r r i s and B e r g e i j k (1962) f o r a d i p o l e s o u r c e . 3 3 d r =A(A /T ) c o s . 9 d r =» t h e r a d i a l d i s p l a c e m e n t . A =" t h e d i s p l a c e m e n t a m p l i -tude o f t h e sound s o u r c e . A = t h e r a d i u s o f t h e sound s o u r c e , r = t h e d i s t a n c e from t h e sound s o u r c e . 6 = t h e a n g l e between th e d e v i c e s e n s i n g t h e v i b r a -t i o n s from the sound s o u r c e , and t h e a x i s o f o s c i l l a t i o n o f t h e sound s o u r c e . I n t h e s e e x p e r i m e n t s A A cos 0 i s a c o n s t a n t =» 0.25 cm.; cos 0 = 1 (because 0 i s approx. 0) ; A = 0.15 cm 2. T h e r e f o r e A A 3 cos 9 = 8.725 x 1 0 ~ 4 - 24 -The d i s p l a c e m e n t t o wh i c h f i s h e s A, B and D responded t o i s g i v e n by d r •» 8.725 x 1CT 4 = 1.7 x 1 0 ~ 3 cms. F i s h C o r i e n t a t e d t o a d i s p l a c e m e n t g i v e n by d r = 8.725 x 1 0 ~ 4 0.6 3 = 4.0 x 1 0 ~ 3 cms. T h e r e f o r e t h e b l i n d g o l d f i s h responded d i r e c t i o n a l l y t o d i s p l a c e m e n t w h i c h v a r i e d between 1.7 x 1 0 ~ 3 cm. and _3 4.0 x 10 cms. i n a m p l i t u d e a t 30 c p s . The g o l d f i s h d i d not respond to t h e 100 c p s . sound s o u r c e . B l i n d cave f i s h responded t o b o t h t h e 100 c p s . and t h e 30 c p s . sound s o u r c e . I n a l l but one case t h e d i s t a n c e a t w h i c h t h e f i s h f i r s t responded t o the s o u r c e was 4.5 cms. d r - 8.725 x 1 0 " 4 4.5 3 = 9.7 x 1 0 " 6 cms. T h e r e f o r e b l i n d cave f i s h respond d i r e c t i o n a l l y t o d i s p l a c e m e n t s of 9.7 x 1 0 ~ 6 cms. i n a m p l i t u d e a t f r e q u e n c i e s o f 30 c p s . and 100 c p s . - 25 -DISCUSSION The r e s u l t s o f the f i r s t p a r t o f the experiment i n d i c a t e t h a t b l i n d cave f i s h a r e b e t t e r a b l e t o l o c a t e s t a t i o n a r y r o d s than b l i n d g o l d f i s h even though t h e r o d s used i n t h e t e s t s t o a s c e r t a i n t h e cave f i s h e s d i r e c t i o n a l a b i l i t y were t h i n n e r . I f t h e g o l d f i s h had f a i l e d t o l o c a t e the r o d s o b s t r u c t i n g t h e i r p a t h s o f l o c o m o t i o n e v e r y time i n t h e f o r t y t e s t s , t h e n i t c o u l d be argued t h a t e i t h e r t h e f i s h had f a i l e d t o sense t h e i r p r e s e n c e o r had sensed them but f a i l e d t o l o c a l i s e them. However, the g o l d f i s h d i d l o c a l i s e t h e r o d s s i x t i m e s o u t o f f o r t y w h i c h i n d i c a t e s t h a t f i s h must have not o n l y sensed t h e r o d s but a l s o l o c a t e d them. I t i s ( t h e r e f o r e , p o s s i b l e t o c o n s i d e r t h a t i n the o t h e r t h i r t y - f o u r t e s t s t h e g o l d f i s h were u n a b l e t o l o c a l i s e t h e r o d s r a p i d l y enough t o t a k e a v o i d i n g a c t i o n . Why t h e n were t h e g o l d f i s h u n a b l e t o make an a v o i d i n g a c t i o n i n t i m e ? The a b i l i t y of t h e f i s h t o a v o i d an o b j e c t depends upon t h e swimming speed of the f i s h as i t approaches t h e r o d , t h e d i s t a n c e away from t h e r o d when th e f i s h i s f i r s t a b l e to d e t e c t i t and t h e r e s p o n s e time o f the f i s h t o c o n v e r t the i n f o r m a t i o n i t r e c e i v e s about t h e p o s i t i o n o f t h e r o d i n t o an a v o i d i n g a c t i o n . I f the p r o d u c t o f t h e approach speed and t h e d i s t a n c e away from t h e r o d at w h i c h t h e f i s h f i r s t d e t e c t s i t , i s g r e a t e r than t h e response t i m e i t w i l l c o l l i d e w i t h t h e r o d . - 26 -The a b i l i t y of f i s h t o d e t e c t o b j e c t s a t a d i s t a n c e by m e c h a n i c a l means has been n o t i c e d by s e v e r a l p e o p l e i n c l u d i n g D i j k g r a a f (1963) who n o t i c e d t h a t b l i n d e d f i s h were a b l e t o d e t e c t t h e approach o f o b j e c t s moved s l o w l y t h r o u g h t h e w a t e r towards them. The organs c r e d i t e d w i t h b e i n g s e n s i t i v e t o t h i s " d i s t a n c e t o u c h " are t h e d i s p l a c e m e n t s e n s i t i v e l a t e r a l l i n e organs and most o f t h e e v i d e n c e r e l a t i n g t o t h e d i s p l a c e m e n t s e n s i t i v i t y o f t h e l a t e r a l l i n e organs has been r e v i e w e d by D i j k g r a a f (1963) who draws e v i d e n c e t o s u p p o r t t h i s c o ncept from b e h a v i o u r a l , m o r p h o l o g i c a l and p h y s i o l o g i c a l s t u d i e s . The l a t e r a l l i n e organs are c o n s i d e r e d n o t o n l y t o be d i s p l a c e m e n t s e n s i t i v e , but are a l s o c o n s i d e r e d t o be d i r e c t i o n a l l y s e n s i t i v e . F l o c k and W e r s a l l (1962) demonstrated f r o m e l e c t r o n m i c r o s c o p i c a l e v i d e n c e , t h a t t h e l a t e r a l l i n e o rgans of f i s h a r e m o r p h o l o g i c a l l y p o l a r i s e d . T h i s e v i d e n c e i s s u p p o r t e d by t h e n e u r o p h y s i o l o g i c a l r e c o r d i n g s o f Sand(1937) i n elasmobranchs, and o t h e r w o r k e r s such as Murray (1955) and D i j k g r a a f (1961) i n am p h i b i a , t h a t a t l e a s t two forms o f a f f e r e n t n e r v e f i b e r s i n n e r v a t e the l a t e r a l l i n e o r g a n s , t h o s e w h i c h f i r e when t h e c u p u l a r o f t h e l a t e r a l l i n e organs i s d e f l e c t e d i n one d i r e c t i o n , and t h o s e w h i c h f i r e when i t i s d e f l e c t e d i n the o p p o s i t e d i r e c t i o n . Thus, t h e l a t e r a l l i n e organs are b o t h m o r p h o l o g i c a l l y and p h y s i o l o g i c a l l y p o l a r i s e d . D i j k g r a a f assumed t h a t f i s h responded t o t h e damming e f f e c t o f the w a t e r b u i l t up ahead of b l u f f b o d i e s as t h e y came c l o s e r t o the f i s h . I t i s a l s o t r u e t h a t swimming f i s h b u i l d up a damming e f f e c t ahead of them as they swim. T h i s has been demonstrated r e c e n t l y by W a l t e r s (1966) who used a p o l a r o m e t r i c method t o o b s e r v e t h e damming phenomena b u i l t up ahead o f b l i n d cave f i s h as t h e y swam. Because t h e f r o n t of t h e head of t h e f i s h i s b l u f f , w a t e r i s f i r s t pushed ahead o f the f i s h b e f o r e i t i s a b l e t o escape t o t h e s i d e . Thus, a swimming f i s h i s l i k e l y t o e x p e r i e n c e a c o n s t a n t d i s p l a c e m e n t o f i t s l a t e r a l l i n e o r g a n s , and i s a b l e , as D i j k g r a a f p u t s i t , . " t o d e t e c t t h e r e s i s t i v i t y o f t h e w a t e r ahead o f t h e f i s h . " I f a r o d i s p l a c e d i n t h e f i e l d o f the damming e f f e c t ( F i g u r e 3b) t h e c o n f i g u r a t i o n o f the bow wave w i l l be d i s t o r t e d , and t h e v e l o c i t y o f t h e w a t e r f l o w between the o b j e c t and the f i s h w i l l i n c r e a s e as w a t e r from t h e bow wave i s f o r c e d to t r a v e l t h r o u g h the r e s t r i c t e d a p e r t u r e . I n t h i s way t h e f i s h would be a b l e t o d e t e c t the o b j e c t e i t h e r by measuring t h e c h a n g i n g c o n f i g u r a t i o n of i t s bow wave, o r by the c h a n g i n g v e l o c i t y o f w a t e r p a s t i t s head, o r by b o t h . A l t h o u g h the b l u f f n e s s o f the g o l d f i s h ' s head i s not as g r e a t as t h a t o f the b l i n d cave f i s h , t h e g r e a t e r s i z e o f t h e g o l d f i s h used i n t h e s e e x p e r i m e n t s means they would send out bow waves ahead o f them of an e x t e n t a t l e a s t as g r e a t as t h o s e s e n t out by the b l i n d cave f i s h . T h i s - 28 -F i g u r e 3 A The bow wave s e t up b l i n d cave f i s h . B The i n t e r r u p t i o n o f o f an o b j e c t i n t h e p a t h o f ahead o f a swimming Mexican t h e bow wave by t h e pr e s e n c e a b l i n d cave f i s h . TOP OF CAVE FISH HEAD - 29 -assumption was i n v e s t i g a t e d l a t e r and found t o be c o r r e c t . The g o l d f i s h i n t h e s e e x p e r i m e n t s t r a v e l l e d a t l e a s t t h r e e t i m e s t h e speed o f the cave f i s h , w h i c h meant th e y c o v e r e d t h e w i d t h o f t h e i r bow wave t h r e e t i m e s as q u i c k l y as the b l i n d cave f i s h , and would, t h e r e f o r e , have o n l y one t h i r d o f t h e time t o respond i n , and t a k e a v o i d i n g a c t i o n , i f an o b j e c t were d e t e c t e d i n i t s bow wave. Thus, i t i s p r o b a b l e t h a t the g o l d f i s h h i t more r o d s t h a n t h e cave f i s h because t h e y had l e s s t ime i n w h i c h t o t a k e a v o i d i n g a c t i o n a f t e r d e t e c t i n g t h e r o d . I n t h e second p a r t o f t h e experiment g o l d f i s h were a b l e t o l o c a t e a sound s o u r c e o f 30 c p s . but were un a b l e t o l o c a t e a s o u r c e o f 100 c p s . T h i s i n d i c a t e s a l i m i t i n g f r e q u e n c y r e s p o n s e i n the organs d e t e c t i n g the v i b r a t i o n s from the sound s o u r c e . As p r e v i o u s l y d i s c u s s e d , i t i s t h e o r e t i c a l l y p o s s i b l e t o d i s c o u n t t h e e a r s as b e i n g a b l e t o l o c a t e sound s o u r c e s under w a t e r . T h i s i s i n d i r e c t l y s u p p o r t e d by one o f t h e r e s u l t s o f t h e s e e x p e r i m e n t s and t h e work of Enger (1966). Enger demonstrated from e l e c t r o -p h y s i o l o g i c a l e x p e r i m e n t s t h a t t h e a c o u s t i c f r e q u e n c y range o f t h e e a r s o f t h e g o l d f i s h e x t e n d o v e r a range o f about 50 c p s . t o s e v e r a l thousand c y c l e s p e r second. T h e r e f o r e , i f t h e g o l d f i s h was c a p a b l e o f u s i n g i t s e a r s f o r l o c a l i s i n g sound s o u r c e s i t s h o u l d have been a b l e t o l o c a l i s e t h e sound s o u r c e at 100 c p s . , but i t f a i l e d t o do s o , and o n l y l o c a l i s e d i t when i t v i b r a t e d at 30 c p s . , w h i c h - 30 -i s b e l i e v e d t o be w i t h i n t h e f r e q u e n c y range o f re s p o n s e o f the l a t e r a l l i n e o r g a n s . The a m p l i t u d e o f t h e n e a r f i e l d d i s p l a c e m e n t s at the p o s i t i o n s n e a r the sound s o u r c e where t h e g o l d f i s h and the b l i n d cave f i s h f i r s t began to t a k e a v o i d i n g a c t i o n were c a l c u l a t e d w i t h t h e i n t e n t i o n of f i n d i n g t h e o r d e r of magnitude o f d i s p l a c e m e n t s t o whi c h t h e f i s h were s e n s i t i v e . I t i s r e a l i s e d t h a t t h e s e v a l u e s may not r e f l e c t t h e t r u e magnitude o f s e n s i t i v i t y o f t h e s e two s p e c i e s , but g o l d f i s h i n p a r t i c u l a r appear t o be s e v e r a l o r d e r s o f magnitude l e s s s e n s i t i v e t o w a t e r d i s p l a c e m e n t t h a n b l i n d cave f i s h . I t i s su g g e s t e d t h a t t h e method by w h i c h t h e s e measurements were made may g i v e an i n d i c a t i o n o f t h e g o l d -f i s h e s r e s p o n s e time o f r e a c t i o n t o t h e sound s o u r c e r a t h e r t h a n i t s d i s p l a c e m e n t s e n s i t i v i t y . F o r i n s t a n c e , t h e g o l d -f i s h used i n t h i s e x periment were many tim e s h e a v i e r and swam a p p r o x i m a t e l y t h r e e t i m e s f a s t e r ( a t 3 cm. s e c . - 1 ) t h a n t h e b l i n d cave f i s h . T h i s i m p l i e s t h a t t h e g o l d f i s h would have more d i f f i c u l t y i n s t o p p i n g and t a k i n g a v o i d i n g a c t i o n t h a n b l i n d cave f i s h because o f t h e i r g r e a t e r momentum. A l s o t h e g o l d f i s h had r e c e n t l y been d e p r i v e d of t h e i r e y e s i g h t and i t i s p r o b a b l e t h a t t h e i r nervous system had n o t y e t compensated f o r t h i s l o s s o f i n p u t . However, i t may be noted t h a t s i m i l a r e x p e r i m e n t s - performed w i t h g o l d f i s h b l i n d e d e i g h t weeks p r e v i o u s l y and h e l d i n t a n k s - y i e l d e d s i m i l a r r e s u l t s . - 31 -I t i s e v i d e n t t h a t , under t h e e x p e r i m e n t a l c o n d i t i o n s imposed upon them, g o l d f i s h and b l i n d cave f i s h a re c a p a b l e o f b o t h d e t e c t i n g s t a t i o n a r y r o d s and low f r e q u e n c y sound s o u r c e s . I n b o t h c a s e s t h e l a t e r a l l i n e o r g a n s , w i t h t h e p o s s i b l e a s s i s t a n c e o f t o u c h r e c e p t o r s , a re i n d i r e c t l y i m p l i c a t e d as t h e organs c a p a b l e o f d i r e c t i o n a l r e s p o n s e . - 32 -BEHAVIOUR:PART 2 Are F i s h a b l e t o l o c a l i s e a Sound Source a g a i n s t C o n s t a n t  Background N o i s e ? INTRODUCTION The p r e v i o u s e x p e r i m e n t s demonstrated t h e a b i l i t y o f b o t h b l i n d cave f i s h and b l i n d g o l d f i s h t o l o c a t e t h e p o s i t i o n s o f s t a t i o n a r y and v i b r a t i n g o b j e c t s . Under t h e s e c i r c u m s t a n c e s t h e o o b j e c t s were l o c a t e d a g a i n s t a background n o i s e o f t h e f i s h ' s own body movements. The p r e s e n t e x p e r i m e n t s were d e s i g n e d t o i n v e s t i g a t e the a b i l i t y o f b l i n d cave f i s h t o l o c a t e sound s o u r c e s a g a i n s t an e x p e r i -m e n t a l l y imposed background n o i s e . A s e r i e s o f t e s t s were d e s i g n e d f i r s t l y t o de t e r m i n e i f t h e f i s h i s a b l e t o d i s t i n g u i s h between c o n c u r r e n t u n i d i r e c t i o n a l , v i b r a t o r y d i s p l a c e m e n t s i n t h e w a t e r , and s e c o n d l y i f a f i s h i s a b l e t o d i s c r i m i n a t e between two v i b r a t o r y d i s p l a c e m e n t waves o r i e n t a t e d i n p l a n e s at r i g h t a n g l e s t o each o t h e r , i n c l u d i n g t e s t s t o show i f f i s h a r e a b l e t o d i s t i n g u i s h between two v i b r a t i o n a l d i s p l a c e m e n t s o r i e n t a t e d a t r i g h t a n g l e s t o each o t h e r and of the same f r e q u e n c y , and s i m i l a r a m p l i t u d e . The experiment i s i n t e n d e d to t e s t t h e d i r e c t i o n a l p r o p e r t i e s o f t h e s e n s o r y system w h i c h the f i s h uses f o r d i r e c t i o n a l l o c a l i z a t i o n . I f t h e f i s h i s a b l e to d i f f e r e n t i -a t e between two d i s p l a c e m e n t waves v i b r a t i n g at r i g h t a n g l e s - 33 -to each o t h e r and i s a b l e t o use t h e c h a r a c t e r i s t i c s o f one o f t h e waves t o l o c a l i s e a sound s o u r c e o r an o b j e c t , t h e n t h e e a r s can be e x c l u d e d from b e i n g c o n s i d e r e d the s e n s o r y system i n q u e s t i o n . T h i s i s because the e a r s respond t o p r e s s u r e waves and would r e c e i v e t h e sum o f t h e two p r e s s u r e waves ( H a r r i s and B e r g e i j k 1962) w h i c h accompany the d i s p l a c e m e n t waves and would be unable t o d e t e r m i n e the d i r e c t i o n o f t r a v e l o f t h e wave. I n o r d e r t o l o c a l i s e an o b j e c t by i n f o r m a t i o n c a r r i e d by t h e p r e s s u r e wave whi c h t r a v e l s p r i m a r i l y i n t h e h o r i z o n t a l p l a n e , t h e f i s h would have t o be c a p a b l e o f b r e a k i n g down the complex ^ p r e s s u r e wave i t d e t e c t s i n t o two components, and t o do t h i s would presume a knowledge of t h e d i r e c t i o n o f t r a v e l o f one o f t h e p r e s s u r e waves. F i g u r e 4 A A di a g r a m o f t h e arrangement o f t h e ap p a r a t u s used i n t h e experiment t o measure t h e a c o u s t i c f i e l d o f t h e sound g e n e r a t e d i n t h e s m a l l tank by t h e e i g h t i n c h l o u d s p e a k e r . B The v i b r a t i o n a l movement o f t h e base o f t h e tank caused by t h e v i b r a t i o n o f t h e diaphragm o f t h e l o u d s p e a k e r . C A q u a d r i p o l a r sound s o u r c e . F o r c e s F ^ F ^ a p p l i e d t o g e t h e r cause t h e sphere t o form an e l l i p s o i d w i t h i t s major a x i s i n t h e v e r t i c a l p l a n e . F o r c e F2F2causes an e l l i p s o i d to be formed w i t h i t s major a x i s i n t h e h o r i z o n t a l p l a n e . N]N 2 and N 3 N 4 r e p r e s e n t two h o r i z o n t a l n o d a l r i n g s . N-^ N^  and N 2N 4 r e p r e s e n t two v e r t i c a l n o d a l r i n g s . The l i n e t h r o u g h NjN 2 i s f o r t h e comparison o f the motion o f t h e sphere above t h i s l i n e w i t h t h e motion o f the base o f the tank . PRE- AMPLIFIER OSCILLOSCOPE QUADRIPOLAR SOUND SOURCE - 35 -EXPERIMENTAL The e x p e r i m e n t s were c a r r i e d out on b l i n d cave f i s h h e l d i n t h e s m a l l aquarium tank d e s c r i b e d i n t h i s p r e v i o u s s e c t i o n . The a p p a r a t u s and e x p e r i m e n t a l p r o c e d u r e s used i n t h e p r e v i o u s experiment were r e t a i n e d f o r t h i s e x p e r i -ment e x c e p t t h a t t h e e x p e r i m e n t s were r e p e a t e d a g a i n s t a c o n s t a n t background n o i s e . The n o i s e was a c h i e v e d by p l a c i n g t h e s m a l l t a n k , c o n t a i n i n g w a t e r at t h e same te m p e r a t u r e as t h e w a t e r i n t h e h o l d i n g tank f o r the b l i n d cave f i s h , d i r e c t l y o v e r t h e diaphragm o f an e i g h t i n c h l o u d s p e a k e r ( F i g u r e 4 a ) . S i n g l e tone s i g n a l s l a s t i n g t h e d u r a t i o n o f each t e s t were d e l i v e r e d t h r o u g h t h i s s p e a k e r from an au d i o g e n e r a t o r v i a an 11 w a t t a m p l i f i e r . The f r e q u e n c y and a m p l i t u d e of the p r e s s u r e wave caused i n t h e w a t e r o f the s m a l l tank was m o n i t o r e d f i r s t on an o s c i l l o s c o p e s c r e e n by r e c o r d i n g t h e v o l t a g e o u t p u t of a s m a l l hydrophone p l a c e d i n t h e w a t e r on t h e t a n k . The hydrophone had p r e v i o u s l y been c a l i b r a t e d by t h e " n u l l d i s p l a c e m e n t " method, f i r s t d e s c r i b e d by T r o t t and L i d e (1955), and was found t o have a f l a t f r e q u e n c y response w i t h an o u t p u t o f 1 m i c r o v o l t p e r m i c r o b a r o v e r a f r e q u e n c y range o f 0-650 c p s . The hydrophone was mounted on a r o d , clamped on the arm o f a m i c r o m a n i p u l a t o r and moved around t h e t a n k , 0 - 36 -measuring t h e hydro-dynamic p r e s s u r e at each p o i n t d e v e l o p e d t h r o u g h o u t t h e t a n k . The diaphragm o f the s p e a k e r o s c i l l a t e d up and down a t f r e q u e n c i e s between 25 and 500 c p s . d u r i n g the t r a n s m i s s i o n o f a tone s i g n a l . These v i b r a t i o n s were conducted t o t h e base of t h e s m a l l aquarium w h i c h a l s o o s c i l l a t e d up and down at t h e same f r e q u e n c y as the s p e a k e r diaphragm. The bottom o f t h e tank a c t e d l i k e a p l u n g e r p u s h i n g t h e w a t e r up and down u n i f o r m l y so t h a t a t any i n s t a n t t h e hydrodynamic p r e s s u r e , and w a t e r d i s p l a c e m e n t was u n i f o r m t h r o u g h o u t the tank. The f l o o r o f the tank was c o n s i d e r e d t o behave i n a s i m i l a r manner t o t h a t o f a q u a d r i p o l a r sound s o u r c e . A q u a d r i p o l a r motion i s produced by a sphere when i t i s c o n s t r i c t e d by two f o r c e s w h i c h a re a p p l i e d t o t h e sp h e r e p e r i o d i c a l l y and a l t e r n a t e l y at r i g h t a n g l e s t o each o t h e r ( F i g u r e 4b and c ) . When F^ i s a p p l i e d the sphere forms an e l l i p s o i d w i t h i t s major a x i s i n t h e v e r t i c a l p l a n e , and when F 2 i s a p p l i e d i t forms an e l l i p s o i d w i t h i t s major 'axis i n t h e h o r i z o n t a l p l a n e . I f F^ -=F2 then t h e sphere w i l l p e r f o r m t h i s o s c i l l a t i o n about 4 n o d a l r i n g s i n d i c a t e d by N 1 N 2 N 3 N 4 ( F i g u r e 4) w h i c h a r e f i x e d and u n a f f e c t e d by the o s c i l l a t i o n s . The base o f the tank shown i n b has a motion s i m i l a r t o t h e motion o f the segment o f t h e sphere u n d e r g o i n g q u a d r i p o l a r o s c i l l a t i o n s demarcated by t h e l i n e , and so i t i s j u s t i f i e d i n a p p l y i n g e q u a t i o n s d e f i n i n g - 37 -q u a d r i p o l a r motion t o t h e motion o f t h e base o f t h e t a n k . The hydrodynamic p r e s s u r e s were r e c o r d e d from t h e tank and c o n v e r t e d i n t o w a t e r d i s p l a c e m e n t v a l u e s by a p p l y i n g t h e e q u a t i o n ( T a b l e V) d e s c r i b i n g t h e r e l a t i o n s h i p between p r e s s u r e and w a t e r d i s p l a c e m e n t i n t h e n e a r f i e l d o f a q u a d r i p o l a r sound s o u r c e H a r r i s (1963). When the a c o u s t i c f i e l d o f t h e s o u r c e of n o i s e had been m o n i t o r e d at v a r i o u s f r e q u e n c i e s , a s e r i e s o f t e s t s were performed t o see i f b l i n d cave f i s h were s t i l l a b l e t o d e t e c t t h e p r e s e n c e o f a r o d p l a c e d i n t h e i r p a t h d e s p i t e the p r e s e n c e o f a background n o i s e . The same p r o c e d u r e was used i n t h e s e e x p e r i m e n t s as was used i n t h e e x p e r i m e n t s where no background n o i s e was p r e s e n t . The f i s h were a l l o w e d t o approach t h e r o d s , o r sound s o u r c e t e n t i m e s f o r each f r e q u e n c y o f t h e background n o i s e used, and t h e r e s u l t s o f t h e b e h a v i o u r o f t h e f i s h under t h e s e c o n d i t i o n s were r e c o r d e d i n t a b u l a r form. - 38 -RESULTS The Measurement o f t h e A c o u s t i c F i e l d o f the N o i s e Source. The hydrodynamic p r e s s u r e changes i n t h e s m a l l tank caused by t h e n o i s e s o u r c e were measured by t h e hydrophone f o r f r e q u e n c i e s o f 25, 50, 100, 200 and 500 c y c l e s p e r second. The a m p l i f i e r i n t e n s i t y l e v e l was k e p t at a f i x e d v a l u e so t h a t power i n p u t t o t h e l o u d s p e a k e r was always c o n s t a n t . I t was found t h a t t h e hydrodynamic p r e s s u r e i n t h e tank was u n i f o r m f o r any p a r t i c u l a r f r e q u e n c y e x c e p t f o r a s m a l l volume of w a t e r n e a r t h e s i d e o f t h e t a n k . F o r c a l c u l a t i o n p u r p o s e s , t h e p r e s s u r e was measured always at a p o i n t 5 cm. above th e c e n t r e o f the f l o o r o f t h e tank because t h i s was t h e h e i g h t a t w h i c h t h e b l i n d cave f i s h u s u a l l y swam. The f r e q u e n c y of t h e n o i s e s o u r c e and the p r e s s u r e and d i s p l a c e m e n t amplitudes g e n e r a t e d i n t h e s m a l l tank were measured o r c a l c u l a t e d and a r e t a b u l a t e d i n T a b l e V. To Determine i f B l i n d Cave F i s h are s t i l l a b l e t o d e t e c t  a Rod p l a c e d i n t h e i r p a t h s d e s p i t e t h e P r e s e n c e o f a  Background N o i s e o f C o n s t a n t A m p l i t u d e and Frequency. Only i n 9 t e s t s o ut o f a t o t a l o f 150 d i d t h e b l i n d cave f i s h f a i l t o l o c a t e v e r t i c a l r o d s p l a c e d i n t h e i r p a t h s d e s p i t e t h e p r e s e n c e o f background n o i s e s w h i c h ranged from 43.5 t o 57.5 d e c i b e l s above 1 m Bar o r , - 39 -i n terms o f d i s p l a c e m e n t , from 0.3 m i c r o n s t o 35 m i c r o n s . The o s c i l l a t i o n s o f the w a t e r caused by t h e background n o i s e were i n the v e r t i c a l p l a n e , where as t h e d i s p l a c e m e n t s caused by the f i s h as i t approached the r o d s were i n t h e h o r i z o n t a l p l a n e . These t e s t s i n d i c a t e t h a t the f i s h were a b l e t o d i s c r i m i n a t e between p e r i o d i c a l l y c h a n g i n g w a t e r d i s p l a c e m e n t s i n t h e v e r t i c a l p l a n e , and u n i d i r e c t i o n a l d i s p l a c e m e n t s i n the h o r i z o n t a l p l a n e . The d i s t a n c e f rom t h e r o d s where t h e f i s h f i r s t made an avo i d a n c e r e a c t i o n was a p p r o x i m a t e l y 0.3 cm. ( T a b l e VI) w h i c h i s o f same d i s t a n c e as i n the t e s t s when t h e r e was no background n o i s e ( T a b l e I I ) . To Determine i f B l i n d Cave F i s h are s t i l l a b l e t o D e t e c t  t h e P r e s e n c e o f a Sound Source p l a c e d i n t h e i r P a t h s d e s p i t e  t h e P r e s e n c e o f a Background N o i s e . B l i n d cave f i s h a r e c l e a r l y a b l e to l o c a t e a v i b r a t i n g bead p l a c e d i n t h e i r p a t h s d e s p i t e t h e p r e s e n c e of a background n o i s e , as i n d i c a t e d by the r e s u l t s t a b u l a t e d i n T a b l e V I I . These r e s u l t s i n d i c a t e t h a t t h e f i s h d i f f e r e n t i a t e between v e r t i c a l o s c i l l a t i o n s , caused by t h e n o i s e s o u r c e , and h o r i z o n t a l o s c i l l a t i o n s o f t h e w a t e r caused by t h e v i b r a t i n g bead w h i c h i s t h e sound s o u r c e s e t i n t h e i r p a t h s o f l o c o m o t i o n . - 40 -TABLE V* The c a l i b r a t i o n o f the p r e s s u r e changes g e n e r a t e d i n t h e s m a l l  tank by background n o i s e f o r d i f f e r e n t f r e q u e n c i e s . Frequency c p s . P r e s s u r e U B a r s D i s p l a c e m e n t Angstroms D e c i b e l S c a l e r e f . t o 1 u Bar 25 150 35,000 43.5 50 250 10,000 47.9 100 350 3,500 50.8 200 600 1,500 55.6 500 750 300 57.5 D e c i b e l s c a l e i s c a l c u l a t e d from t h e r e l a t i o n s h i p n => 20 Log P I 10 P2 n=n d e c i b e l s P]_=» measured p r e s s u r e ~?2~ r e f e r e n c e p r e s s u r e The sound s o u r c e used f o r t h e background n o i s e was c o n s i d e r e d t o be an approximate q u a d r i p o l a r s o u r c e , t h e r e f o r e t h e r e l a t i o n below was used to o b t a i n t h e d i s p l a c e m e n t caused by t h e sound s o u r c e and s e t up i n the w a t e r o f t h e t a n k . 477* % f p c where c / f t h e r e f o r e d — 477V f 2 p F o r t h i s e x periment r a 5 c m s . p = l gm. cm." 3 d P r P d i s p l a c e m e n t i n cms. p r e s s u r e i n u B a r s , d i s t a n c e o f p o i n t o f measurement from sound s o u r c e i n cms. f r e q u e n c y i n c p s . d e n s i t y o f w a t e r . - 41 -TABLE VIU The e f f e c t o f n o i s e oft c o n s t a n t a m p l i t u d e and f r e q u e n c y on t h e a b i l i t y o f b l i n d cave f i s h t o d e t e c t a r o d p l a c e d i n t h e i r p a t h . N o i s e Frequency c p s . F i s h I d e n t i -f i c a t i o n No. of Approaches No. o f A v o i d -ances N e a r e s t D i s t a n c e o f Approach 25 1 10 10 0.3 cm. 2 10 10 0.3 cm. 3 10 10 0.3 cm. 50 1 10 10 0.3 cm. 2 10 9 0.3 cm. 3 10 10 0.3 cm. 100 1 10 7 0.3 cm. 2 10 10 0.3 cm. 3 10 10 0.3 cm. 200 1 10 10 0.3 cm. 2 10 10 0.3 cm. 3 10 8 0.3 cm. 500 1 10 9 0.3 cm. 1 2 10 8 0.3 cm. 3 10 10 0.3 cm. + 0.1 cm. Diameter o f r o d s 5 3 0.3 cms. - 42 -TABLE V I I . The e f f e c t o f n o i s e o f c o n s t a n t a m p l i t u d e and f r e q u e n c y on t h e a b i l i t y o f b l i n d cave f i s h to d e t e c t a v i b r a t i n g bead p l a c e d i n t h e i r p a t h . Frequency c p s . F i s h I d e n t i -f i c a t i o n No. o f Approaches No. o f A v o i d -ances N e a r e s t D i s t a n c e o f Approach 25 1 10 10 4.5 cm. 2 10 10 4.4 cm. 3 10 10 4.5 cm. 50 1 10 10 4.5 cm. 2 10 10 4.6 cm. 3 10 10 4.9 cm. 100 1 10 10 4.4 cm. 2 10 10 4.5 cm. 3 10 10 u 4.5 cm. 200 1 10 10 4.6 cm. 2 10 10 4.5 cm. 3 10 10 4.5 cm. 500 1 10 10 4.5 cm. 2 10 10 4.5 cm. 3 10 10 4.5 cm. + 0 . 1 cm. Di a m e t e r o f g l a s s bead = 0.15 cms. A m p l i t u d e o f v i b r a t i o n = 0.4 cms. Frequency o f v i b r a t i o n => 100 c p s . A m p l i t u d e o f wa t e r d i s p l a c e m e n t 4.5 cms. from g l a s s bead. = 9.7 x 10-6 - 970.0 A° - 43 -They are a b l e t o l o c a t e t h e sound s o u r c e independent o f t h e f r e q u e n c y o f t h e background n o i s e , even i n t h e c a s e where t h e f r e q u e n c y o f t h e background n o i s e i s t h e same as t h e sound s o u r c e , and t h e a m p l i t u d e o f the w a t e r d i s p l a c e m e n t s caused by t h e background n o i s e are f o u r t i m e s t h o s e caused by t h e sound s o u r c e . A l s o , the s e n s i t i v i t y o f t h e cave f i s h t o t h e sound s o u r c e was not i m p a i r e d by t h e p r e s e n c e of the n o i s e as can be seen by comparing t h e n e a r e s t d i s t a n c e s o f approach t o t h e sound s o u r c e g i v e n i n T a b l e s IV and V I I . - 44 -DISCUSSION B l i n d cave f i s h p o s s e s s a f a c i l i t y f o r l o c a t i n g o b j e c t s and a sound s o u r c e a g a i n s t a background n o i s e , a c c o r d i n g t o r e s u l t s drawn from t h e s e e x p e r i m e n t s . T h i s a b i l i t y c o u l d be d i s c u s s e d i n terms o f t h e f i s h ' s a b i l i t y t o d e t e c t p r e s s u r e s a g a i n s t background p r e s s u r e s o r i n terms o f d i s p l a c e m e n t because b o t h a c o u s t i c phenomena are p r e s e n t i n t h e e x p e r i m e n t a l c o n d i t i o n s , and t h e f i s h r espond t o b o t h o f them. The p r e s s u r e a t any p o i n t i n t h e e x p e r i m e n t a l tank would c o n s i s t o f components from a l a r g e number o f s o u r c e s . Under t h e e x p e r i m e n t a l c o n d i t i o n s a p r e s s u r e wave would be g e n e r a t e d from the f l o o r o f the tank w h i c h i s the s o u r c e o f background n o i s e , and t h i s i n t u r n would produce r e f l e c t e d waves from t h e w a l l s and f l o o r o f t h e t a n k . C o n s i d e r i n g the d i m e n s i o n s o f t h e e x p e r i m e n t a l tank the r e f l e c t e d p r e s s u r e waves would be h a r d l y a t t e n u a t e d a t t h e f r e q u e n c i e s o f sound used. The f i s h would produce p r e s s u r e waves g e n e r a t e d by i t s own body movements, and t h e s e i n t u r n would i n t e r a c t w i t h o b j e c t s p l a c e d i n the tank as w e l l as t h e w a l l s o f t h e tank and produce component waves. These waves would then i n t e r a c t t o produce a p r e s s u r e w i t h magnitude o n l y and no d i r e c t i o n . P h y s i c a l l y t h e f i s h w i t h i t s s i n g l e swim b l a d d e r would be u n a b l e t o l o c a t e t h e s o u r c e s o f t h e s e p r e s s u r e waves. The d i s p l a c e m e n t o f w a t e r at any one p o i n t i n t h e tan k would be t h e sum o f d i s p l a c e m e n t waves o r i g i n a t i n g from - 45 -t h e same s o u r c e s as the p r e s s u r e waves. But t h e c o n t r i b u t i o n s o f r e f l e c t e d d i s p l a c e m e n t waves, from t h e s i d e s and s u r f a c e o f the t a n k , would c o n t r i b u t e t o t h e r e s u l t a n t d i s p l a c e m e n t t o a f a r l e s s e r e x t e n t t h a n d i d t h e r e f l e c t e d p r e s s u r e waves t o t h e r e s u l t a n t p r e s s u r e . T h i s i s because of t h e r a p i d a t t e n u a t i o n o f d i s p l a c e m e n t waves w i t h d i s t a n c e from a sound s o u r c e . At any p o i n t i n t h e tank a r e s u l t a n t d i s p l a c e -ment wave p o s s e s s i n g both magnitude and d i r e c t i o n may be d e t e c t e d . As p r e v i o u s l y mentioned, t h e l a t e r a l l i n e organs of f i s h and amphibians are d i r e c t i o n a l l y s e n s i t i v e . Sand (1937) demonstrated t h a t l a t e r a l l i n e organs i n Rays a r e o n l y s e n s i t i v e t o d i s p l a c e m e n t s o f w a t e r a l o n g the l o n g a x i s o f t h e l a t e r a l l i n e c a n a l s , and D i j k g r a a f (1956) showed t h a t t h e l a t e r a l l i n e organs o f Xenopus are s e n s i t i v e o n l y t o d i s p l a c e -ments d i r e c t e d a l o n g t h e s t i t c h o f neuromasts w h i c h compose the l a t e r a l l i n e o r g a n . B l i n d cave f i s h have l a t e r a l l i n e organs a r r a y e d i n l i n e s p a r a l l e l t o t h e l o n g a x i s o f the body, f o r example the main t r u n k l a t e r a l l i n e , and o t h e r l i n e s o f o r g a n s , such as t h e h y o m a n d i b u l a r , are a r r a y e d a t r i g h t a n g l e s t o t h i s . A s i n g l e l a t e r a l l i n e o r g a n , depending upon i t s o r i e n t a t i o n on t h e f i s h w i l l r espond o n l y t o one p a r t i c u l a r component of any compound d i s p l a c e m e n t i n t h e w a t e r about t h e f i s h . The f i s h (as a whole) has, t h e r e f o r e , t h e f a c i l i t y t o a n a l y s e c o m p l i c a t e d compound d i s p l a c e m e n t waves i m p i n g i n g upon i t , i n t o t h e s e p a r a t e component waves wh i c h are o r i e n t a t e d i n t o h o r i z o n t a l and v e r t i c a l components. T h i s - 46 -system would be more th a n adequate f o r the f i s h used i n t h e s e e x p e r i m e n t s , and under th e c o n d i t i o n s t o w h i c h t h e y were exposed. They would be a b l e t o d i s c e r n between t h e v e r t i c a l l y o s c i l l a t i n g background d i s p l a c e m e n t s , and t h e h o r i z o n t a l d i s p l a c e m e n t s emanating from t h e sound s o u r c e o r the h o r i z o n t a l d i s p l a c e m e n t caused as a r e s u l t o f t h e i n t e r a c t i o n between th e f i s h e s bow wave and a s t a t i o n a r y o b j e c t i n i t s p a t h . H a v i n g made t h i s s e p a r a t i o n t h e f i s h would then be i n a p o s i t i o n t o l o c a l i s e s o u r c e s c o n t r i b u t i n g to d i s p l a c e m e n t s i n both t h e v e r t i c a l and h o r i z o n t a l p l a n e s . I f t o u c h r e c e p t o r s o n l y were c o n s i d e r e d t o be i n v o l v e d i n l o c a l i s i n g t h e sound s o u r c e , then s e v e r a l d i f f i c u l t i e s would be i n c u r r e d . F i r s t l y , e l e c r o p h y s i o l o g i c a l e v i d e n c e on t o u c h r e c e p t o r s i n f i s h e s i s s c a r c e and i t has to be assumed t h a t t h e y p o s s e s s p r o p e r t i e s s i m i l a r t o t h o s e found i n h i g h e r v e r t e b r a t e s . Namely, t h e y respond i n an " a l l o r none" manner, so t h a t t h e y g i v e o n l y one ungraded re s p o n s e t o an above t h r e s h o l d s t i m u l u s . They are none-d i r e c t i o n a l , and t h e y are q u i c k l y a d a p t i n g . T h e r e f o r e , t h e d i r e c t i o n o f t h e s o u r c e g i v i n g o ut d i s p l a c e m e n t waves can o n l y be a s c e r t a i n e d c e n t r a l l y by t h e f i s h . The b r a i n must a n a l y z e t h e number of t o u c h r e c e p t o r s f i r i n g a l l o v e r i t s body, and f i n d t h e l o c a t i o n where th e g r e a t e s t d e n s i t y o f f i r i n g i s t o be f o u n d . A m p l i t u d e c o u l d be a s c e r t a i n e d o n l y by d e t e c t i n g t h e t o t a l number of t o u c h r e c e p t o r s f i r i n g i n a p a r t i c u l a r 47 -a r e a . Frequency d e t e c t i o n by t h e t o u c h r e c e p t o r s would depend upon th e a d a p t a t i o n r a t e o f r e c e p t o r s , t h e i n f o r m a t i o n c a r r y i n g c a p a c i t y o f t h e n e r v e s t o t h e t o u c h r e c e p t o r s , and t h e p r e s e n c e o f an a s s o c i a t i o n c e n t r e i n the b r a i n c a p a b l e o f r e c o g n i z i n g f r e q u e n c y . I t i s p o s s i b l e t h a t under th e c o n d i t i o n s of t h i s e x periment t h e f i s h may have r a p i d l y adapted t o t h e c o n s t a n t background n o i s e and have d e t e c t e d changes i n the a m p l i t u d e o f v i b r a t i o n s from t h e sound s o u r c e . T h i s i s u n l i k e l y i n t h e s p e c i a l c a s e where th e background n o i s e was e x a c t l y t h e same f r e q u e n c y as t h e sound s o u r c e . Under t h e s e c i r c u m s t a n c e s i f the f i s h adapted t o f r e q u e n c y , i t s h o u l d not have l o c a t e d t h e sound s o u r c e and s h o u l d have been i n s e n s i b l e t o i t . I t i s c o n c l u d e d t h a t t h e e v i d e n c e drawn from t h e s e e x p e r i m e n t s e x c l u d e s t h e e a r s from b e i n g d i r e c t i o n a l r e c e p t o r s and i m p l i c a t e s the l a t e r a l l i n e organs as t h e p r o b a b l e c a n d i d a t e s . Touch r e c e p t o r s cannot be i g n o r e d but appear t o be u n l i k e l y c a n d i d a t e s as d i r e c t i o n a l r e c e p t o r s c a p a b l e o f l o c a t i n g a sound s o u r c e . 1-- 48 -NEUROPHYSIOLOGY:PART I  INTRODUCTION A n a t o m i c a l e v i d e n c e was p r e s e n t e d f i r s t t o show the e x i s t e n c e of an e f f e r e n t nervous s u p p l y t o t h e h a i r ' c e l l s o f t h e mammalian c o c h l e a r by Rasmussen (1946). He t r a c e d n e r v e f i b e r s w h i c h o r i g i n a t e d i n t h e s u p e r i o r o l i v a r y n u c l e u s o f one s i d e o f t h e b r a i n , and c r o s s e d t o t h e c o n t r a l a t e r a l v e s t i b u l a r n erve which they accompanied to the i n t r a g a n g l i o n i c s p i r a l b undle o f the c o c h l e a r . He demonstrated t h e e f f e r e n t n a t u r e o f t h e s e f i b e r s by making a p p r o p r i a t e p l a c e d l e s i o n s i n them and o b s e r v e d t h e i r n ervous d e g e n e r a t i o n towards the c o c h l e a r . The e f f e r e n t f i b e r t r a c t was named the c r o s s e d o l i v o - c o c h l e a r b u n d l e . L a t e r , i n 1960 he was a b l e t o demonstrate t h e e x i s t e n c e o f a f f e r e n t f i b e r s t o t h e c o c h l e a r w h i c h o r i g i n a t e d i n t h e i p s i l a t e r a l s u p e r i o r o l i v a r y n u c l e u s . Galambos (1956) was t h e f i r s t t o i n v e s t i g a t e t h e n e u r o p h y s i o l o g y o f the c r o s s e d o l i v o - c o c h l e a r b u n d l e . He s u b s t a n t i a t e d Rasmussen*s a n a t o m i c a l e v i d e n c e by f i n d i n g them t o be e f f e r e n t f i b e r s , and a l s o he found them t o be s t r o n g l y i n h i b i t o r y . Sound evoked p o t e n t i a l s g e n e r a t e d i n t h e a f f e r e n t v e s t i b u l a r n erve were s t r o n g l y i n h i b i t e d by e l e c t r i c a l s t i m u l a t i o n o f t h e c r o s s e d o l i v o - c o c h l e a r f i b e r s . T h i s i n v e s t i g a t i o n was pursued f u r t h e r by Fex (1962) and - 49 -Desmedt (1960)(1962) who s e p a r a t e l y showed t h a t thennervous a c t i v i t y o f the o l i v o - c o c h l e a r f i b e r s c o u l d be i n c r e a s e d by s t i m u l a t i n g t h e i p s i l a t e r a l e a r by sound, and t h a t t h i s a c t i v i t y c o u l d be f u r t h e r i n c r e a s e d , t h e y b e l i e v e f a c i l i t a t e d , by e l e c t r i c a l l y s t i m u l a t i n g t h e v e s t i b u l a r n e r v e s of t h e c o n t r a l a t e r a l e a r . Fex (1962) c o n s i d e r e d t h e e f f e r e n t s t o be p a r t o f a mechanism f o r feedback c o n t r o l o f t h e s e n s i t i v i t y o f t h e c o c h l e a r t o sound. B o t h w o r k e r s r e a l i s e d t h a t the e f f e r e n t s coded the i n f o r m a t i o n c a r r i e d by the a f f e r e n t v e s t i b u l a r n e r v e , and Desmedt thought i t was i m p o r t a n t t o see how t h e e f f e r e n t s were r e l a t e d t o p s y c h o p h y s i o l o g i c a l problems o f c o n s c i o u s a u d i t o r y p e r c e p t i o n . I n p a r t i c u l a r how an a n i m a l c o u l d d e t e c t a s e r i e s o f complex sounds from a background n o i s e . The p r e s e n c e o f an e f f e r e n t nervous s u p p l y t o t h e h a i r c e l l s of t h e mammalian c o c h l e a r i n v i t e d i n v e s t i g a t i o n s o f o t h e r h a i r c e l l systems t o see i f t h e y too p o s s e s s e d e f f e r e n t i n n e r v a t i o n . I n 1962 F l o c k and W e r s a l l d e s c r i b e d two t y p e s o f i n n e r v a t i o n t o t h e h a i r c e l l s o f t h e l a t e r a l l i n e organs of t h e cottid,, L o t a v u l g a r i s . One t y p e o f n e r v e synapsed onto th e h a i r c e l l w i t h a v e s i c u l a t e d synapse and t h e o t h e r t y p e p o s s e s s e d an u n v e s i c u l a t e d synapse, and v e s i c l e s and g r a n u l e s were p r e s e n t i n t h e c y t o p l a s m o f the h a i r c e l l i n t h e r e g i o n o f t h i s synapse. F l o c k (1966) i n f e r r e d f r om h i s e v i d e n c e t h a t the u n v e s i c u l a t e d synapses - 50 -might be e f f e r e n t , but c o u l d o f f e r no a s s u r a n c e t h a t t hey were n o t r e c u r r e n t c o l l a t e r a l s from a f f e r e n t f i b e r s . From the p r e v i o u s b e h a v i o u r e x p e r i m e n t s i t does appear t h a t f i s h p o s s e s s a f a c i l i t y f o r l o c a l i s i n g a p a r t i c u l a r sound from a background n o i s e . Desmedt and Fex r e a l i s e d t h a t t e r r e s t i a l mammals p o s s e s s t h i s f a c i l i t y , and from t h e i r e x p e r i m e n t a l r e s u l t s i m p l i c a t e d t h e o l i v o c o c h l e a r e f f e r e n t b u n d l e as p a r t o f a mechanism f o r n e u r o p h y s i o l o g i c a l l y s u p p r e s s i n g t h e e f f e c t o f background n o i s e . F l o c k and W e r s a l l ' s . d i s c o v e r y of a p o s s i b l e e f f e r e n t nervous s u p p l y to t h e l a t e r a l l i n e o rgans of f i s h has prompted t h i s p r e s e n t h e u r o p h y s i o l o g i c a l i n v e s t i g a t i o n t o see i f e f f e r e n t s i n n e r v a t i o n t o t h e h a i r c e l l s o f the l a t e r a l l i n e organs does e x i s t and t o see what r o l e , i f any, p l a y s i n overcoming p s y c h o p h y s i o l o g i c a l problems a s s o c i a t e d w i t h a u d i t o r y p e r c e p t i o n i n f i s h e s . . - 51 -EXPERIMENTAL The e x p e r i m e n t s were c a r r i e d o u t on f i f t y g o l d f i s h ( C a r r a s s i u s a u r a t u s ) o f a p p r o x i m a t e l y s i x i n c h e s i n l e n g t h . The f i s h were k e p t p r i o r t o t h e experiment i n l a r g e h o l d i n g t a n k s and were f e d on a reduced d i e t i n o r d e r to l i m i t t h e d e p o s i t i o n o f f a t on t h e b o d i e s o f g o l d f i s h , p a r t i c u l a r l y about t h e o r b i t s . A f i s h was s e l e c t e d f rom t h e h o l d i n g tank and p l a c e d i n a clamp w h i c h h e l d t h e f i s h r i g i d l y f o r the d u r a t i o n o f t h e e x p e r i m e n t . T h i s clamp ( F i g u r e 5a) c o n s i s t s o f a shaped p l a t e 3 of / " p e r s p e x t o t h e m i d d l e o f one s i d e of wh i c h i s screwed 16 a s a d d l e shaped p i e c e d f p e r s p e x . The f i s h ' s body was p l a c e d a c r o s s t h e s a d d l e and t h e t a i l clamped to t h e r e c t a n g u l a r end o f the p l a t e . The head was clamped t o t h e o t h e r end o f t h e p l a t e by means of a p l a s t i c tube w h i c h was i n s e r t e d i n t o t h e mouth. T h i s tube was a l s o clamped t o t h e p l a t e . The head end o f t h e p l a t e was c u t away so t h a t t h e o r b i t on the s i d e o f t h e f i s h a d j a c e n t t o the p l a t e was a c c e s s a b l e f o r o p e r a t i o n . The f i s h clamp was th e n a t t a c h e d t o a p l a t f o r m mounted i n t h e o p e r a t i n g tank by means o f a b o l t t h r o u g h a h o l e i n a p i e c e o f p e r s p e x w h i c h was a t t a c h e d t o t h e clamp and s e r v e d as a base. The p e r s p e x o p e r a t i n g tank ( F i g u r e 5b) had a p e r s p e x p l a t f o r m J" t h i c k at one end, 2" below t h e top edge o f t h e t a n k . I n t h e m i d d l e o f t h e p l a t f o r m was a b o l t - 52 -F i g u r e 5 A The clamp used f o r h o l d i n g t h e f i s h r i g i d l y t h r o u g h o u t t h e e x p e r i m e n t . B Schematic arrangement o f the a p p a r a t u s used d u r i n g t h e n e u r o p h y s i o l o g i c a l e x p e r i m e n t s . i PLASTIC SADDLE ELASTIC BAND INLET TUBE CLAMP WATER INLET * TUBE PLASTIC PLATE TAIL CLAMP OSCILLOSCOPE RECORDING ELECTRODE MECHANO-ELECTRIC TRANSDUCER WATER LEVEL WATER COOLER PUMP PERSPEX TANK -VARIABLE TRANSFORMER - 5 3 -f o r s e c u r i n g the clamp. At t h e end o f t h e t a n k , o p p o s i t e th e p l a t f o r m , t h e r e were t h r e e tubes w h i c h p i e r c e d t h e w a l l s o f t h e t a n k . One t u b e , t h e w a t e r i n l e t , was s i t u a t e d i n t he end w a l l , w h i l e t h e o t h e r two tubes were s i t u a t e d on the l o wer edges o f t h e s i d e w a l l s t h r e e i n c h e s from t h e end w a l l s , and were the d r a i n a g e t u b e s . The clamp was b o l t e d t o t h e p l a t f o r m and a f l e x i b l e p l a s t i c tube was connected between t h e tube i n t h e f i s h * s mouth and t h e w a t e r i n l e t t u b e . D e c h l o r i n a t e d w a t e r was c i r c u l a t e d t h r o u g h t h e tank by a s m a l l r o t a r y pump d r i v e n by an e l e c t r i c motor w i t h a v a r i a b l e speed c o n t r o l . The passage of w a t e r i n t h e system was t h r o u g h t h e i n l e t t ube, o v e r t h e f i s h ' s g i l l s , o u t t h r o u g h t h e d r a i n a g e p i p e s , i n t o the pump, t h r o u g h a c o l d w a t e r c o o l i n g c o i l , and back a g a i n t o t h e f i s h . The w a t e r l e v e l i n the tank was c o n t r o l l e d by a d d i n g more w a t e r t o t h e tank o r by d r a i n i n g w a t e r o f f t h r o u g h a t a p . B e f o r e each experiment f r e s h w a t e r was added t o t h e system. Care was t a k e n not t o r a i s e the wa t e r l e v e l above t h e lo w e r edge o f t h e o r b i t so p r e v e n t i n g w a t e r from coming i n c o n t a c t w i t h t i s s u e exposed by d i s s e c t i o n . A d r a w i n g o f the c o m p l e t e l y d i s s e c t e d p r e p a r a t i o n has been g i v e n i n F i g u r e 6 and i s t h e r e s u l t of 26 d i s s e c t i o n s . A l l d i s s e c t i o n was performed under a Z e i s s o p e r a t i n g m i c r o s c o p e w i t h f l o o r s t a n d . The f i s h ' s eye on one s i d e was f i r s t removed by c u t t i n g t h r o u g h t h e o p t i c muscles and t h e o p t i c n e r v e , C o n n e c t i v e t i s s u e and f a t t y t i s s u e was removed from t h e w a l l s o f t h e o r b i t by d i s s e c t i o n and a s p i r a t i o n . Care was - 54 -F i g u r e 6 Diagram o i t h e d i s s e c t e d ramus b u c c a l i s f a c i a l i s on the r i g h t s i d e o f t h e head of a g o l d f i s h . N-^ -N-^ Q r e p r e s e n t l a t e r a l l i n e organs i n t h e " s u b - o r b i t a l l a t e r a l l i n e c a n a l . N - j j L-N - j^represent l a t e r a l l i n e organs i n the n a s a l c a n a l . - 55 -t a k e n not t o d i s t u r b b l o o d v e s s e l s o r n e r v e s , a l t h o u g h i n e v i t a b l y some b l o o d v e s s e l s , such as t h e r e t i n u l a r a r t e r y were c u t . When t h e o r b i t had been d e a l t w i t h i n t h i s manner, b l o o d and l o o s e p i e c e s o f t i s s u e were washed away w i t h oxygenated C a u t l a n d ' s s a l i n e w h i c h was a t t h e same t e m p e r a t u r e as the w a t e r f l o w i n g i n t h e o p e r a t i n g t ank. The f i r s t sub o r b i t a l bone was s e v e r e d from i t s u n d e r l y i n g c o n n e c t i v e t i s s u e and removed from t h e s k u l l . An i n c i s i o n was nex t made i n t h e l a c h r y m a l bone a l o n g a l i n e A-A ( F i g u r e 6) d i v i d i n g t h e bone i n t o two h a l v e s . The l o w e r h a l f o f t h e l a c h r y m a l and t h e second s u b - o r b i t a l bone were r e f l e c t e d back i n one p i e c e , and any u n d e r l y i n g c o n n e c t i v e o r mu s c u l a r t i s s u e impeding t h i s r e f l e c t i o n were c u t . The r e f l e c t e d p o s i t i o n o f t h e s e two bones was m a i n t a i n e d by a f i n e hook r e t r a c t o r . T h i s i n i t i a l d i s s e c t i o n r e v e a l e d t h r e e branches of t h e b u c c a l branch o f t h e f a c i a l n e r v e , t h e s e have been termed branches X, Y and Z i n F i g u r e 6 H e r r i c k (1899) was c o n s u l t e d i n o r d e r t o h e l p i d e n t i f y t h e v a r i o u s nervous components o f t h e o r b i t . * The u s u a l p r o c e d u r e was t o s e l e c t one o f t h e branches X, Y o r Z, and f r e e i t from t h e u n d e r l y i n g c o n n e c t i v e t i s s u e , and f o l l o w t h e ne r v e branch u n t i l i t d i s a p p e a r e d as t h i n f i b e r s t h r o u g h t h e boney w a l l of t h e l a t e r a l l i n e c a n a l i t i n n e r v a t e d . O n l y t h e b u c c a l branches o f t h e f a c i a l - 56 -F i g u r e 7 Schematic arrangement of e l e c t r o n i c r e c o r d -i n g a p p a r a t u s and s t i m u l a t i n g a p p a r a t u s used i n the n e u r o p h y s i o l o g i c a l e x p e r i m e n t s . STIMULATOR OSCILLOSCOPE TRIGGER & UPPERS BEAM LOWER BEAM POWER SUPPLY STIMULUS JSOLATION UNIT STIMULATING "ELECTRODE RECORDING ELECTRODE PRE-AMPLIFIER LOUD SPEAKER AUDIO-AMPLIFIER DUAL TRACK TAPE RECORDER - 57 -nerve i n n e r v a t e d t h e neuromasts o f t h e s u b - o r b i t a l c a n a l and p a r t s of t h e n a s a l c a n a l , and i t was p o s s i b l e t o t r a c e the n e r v e s u n t i l t h e y s p l i t up at t h e base o f each o r g a n . Throughout t h e c l e a r i n g p r o c e s s , c a r e was t a k e n t o e nsure t h a t t h e n e r v e s were always k e p t m o i s t w i t h s a l i n e . When one n e r v e branch t o an organ had been c l e a r e d , v e r y c a r e f u l l y t o p r e v e n t damage t o i t by s c r a p i n g o r s t r e t c h i n g , r e c o r d i n g e l e c t r o d e s were s l i p p e d c a r e f u l l y under t h e n e r v e . S a l i n e was removed from around the e l e c t r o d e s and n e r v e s by a s p i r a t i o n and p a r a f f i n o i l p i p e t t e d i n t o t h e o r b i t and o v e r t h e e l e c t r o d e s t o a c t b o t h as an i n s u l a t o r and t o reduce d e s s i c a t i o n o f t h e n e r v e s . When a c t i v i t y had been found ( i n a nerve branch) t h e w a t e r l e v e l i n t h e tan k was r a i s e d t o c o v e r t h e l a t e r a l l i n e organ i n n e r v a t e d by t h e n e r v e branch from w h i c h r e c o r d i n g s were b e i n g made. A s c h e m a t i c diagram of t h e r e c o r d i n g a p p a r a t u s used i n t h e s e e x p e r i m e n t s has been g i v e n i n F i g u r e 7. The e l e c t r o d e s used i n t h e s e e x p e r i m e n t s were d i f f e r e n t i a l l y r e c o r d i n g e l e c t r o d e s . One t y p e c o n s i s t e d of a p a i r o f p a r a l l e l f i n e s i l v e r w i r e hooks w h i c h were s h i e l d e d c l o s e t o t h e i r t i p s , and mounted on a t h i n p e r s p e x r o d . The s h i e l d i n g was c o n t i n u e d as t h e ground e l e c t r o d e , w h i c h was c l i p p e d onto t h e f i s h . The p e r s p e x r o d was clamped i n t o the arm o f a Palmer m i c r o m a n i p u l a t o r . A n o t h e r type o f - 58 -e l e c t r o d e was used f o r e x t r e m e l y f i n e n e r v e f i b e r s o f s h o r t l e n g t h . T h i s c o n s i s t e d o f a v e r y f i n e p l a t i n u m hook w h i c h was p l a c e d under t h e n e r v e , a f i n e s i l v e r w i r e i n d i f f e r e n t e l e c t r o d e p l a c e d i n t h e t i s s u e c l o s e t o t h e n e r v e , and a ground e l e c t r o d e w h i c h was c l i p p e d t o t h e f i s h . The e l e c t r o d e s were co n n e c t e d by d o u b l e c o r e d , s c r e e n e d c a b l e t o t h e i n p u t o f a d i f f e r e n t i a l l y b a l a n c e d p r e - a m p l i f i e r . The f r e q u e n c y r e s p o n s e o f t h e a m p l i f i e r , a T e k t r o n i x 122, was s e t t o r e j e c t a l l s i g n a l s g r e a t e r t h a n 10,000 c p s . o r l e s s t h a n 80 c p s . , and the g a i n was s e t a t 1000. The o u t p u t o f t h e p r e - a m p l i f i e r was f e d i n t o one c h a n n e l o f a T e k t r o n i x 502A d u a l beam o s c i l l o s c o p e , and a l s o i n t o one c h a n n e l o f a Tanberg s t e r i o A.C. tape r e c o r d e r . One experiment r e q u i r e d t h e use o f an e l e c t r i c a l p u l s e g e n e r a t o r f o r s t i m u l a t i n g the n e r v e s . A G r a s s S4 s t i m u l a t o r was used, and t h i s c o u l d d e l i v e r b oth D.C. and square wave p u l s e s w i t h v a r i a b l e a m p l i t u d e , f r e q u e n c y d u r a t i o n and d e l a y . T h i s machine had t h r e e o u t p u t l e a d s ; two t o t h e o s c i l l o s c o p e , one o f w h i c h m o n i t o r e d t h e i m p u l s e s i g n a l , and the o t h e r w h i c h t r i g g e r e d t h e ti m e base o f t h e o s c i l l o s c o p e . The t h i r d l e a d was t h e s t i m u l a t i o n l e a d and t h i s f e d i n t o a s t i m u l u s i s o l a t i o n u n i t , a Grass S.U.4. The purpose of t h i s t r a n s f o r m e r d e v i c e was t o reduce s t i m u l u s a r t i f a c t by r a i s i n g t h e s t i m u l a t i n g c u r r e n t above ground. The s t i m u l a t i n g c u r r e n t was d e l i v e r e d t h r o u g h two f i n e s i l v e r - 59 -hooks s e t c l o s e t o g e t h e r , about 0.5 mm. a p a r t , and mounted on a p e r s p e x r o d w h i c h was clamped i n t h e arm o f a Palmer m i c r o m a n i p u l a t o r . S e l e c t e d r e s u l t s were photographed w i t h a P o l a r o i d T e k t r o n i x C12 o s c i l l o s c o p e camera mounted on t h e o s c i l l o s c o p e . I n f o r m a t i o n s t o r e d on tape was p l a y e d back t h r o u g h the o s c i l l o s c o p e , a n a l y s e d and photographed at t h e end o f the e x p e r i m e n t . 0 - 60 -RESULTS E v i d e n c e o f an E f f e r e n t Nervous Supply t o t h e L a t e r a l L i n e  Organs i n t h e L a t e r a l L i n e C a n a l s i n t h e Head o f G o l d f i s h . A t o t a l o f e l e v e n f i s h was used i n t h e s e e x p e r i m e n t s . I n i t i a l l y a branch o f t h e f a c i a l n e rve s u p p l y i n g , o r a p p e a r i n g to s u p p l y , a l a t e r a l l i n e organ was s e l e c t e d , and s i l v e r o r p l a t i n u m b i p o l a r r e c o r d i n g e l e c t r o d e s were s l i p p e d under i t . I n each c a s e an i r r e g u l a r spontaneous d i s c h a r g e was r e c o r d e d from t h e n e r v e . The ne r v e was c u t and r e c o r d i n g s made o f any a c t i v i t y i n t h e p r o x i m a l p a r t of t h e n e r v e . V i g o r o u s a c t i v i t y u s u a l l y was n o t i c e d i m m e d i a t e l y a f t e r c u t t i n g the n e r v e s , and t h i s was thought t o be i n j u r y p o t e n t i a l s w h i c h had come about as a r e s u l t o f t h e ne r v e s e c t i o n . However, t h e s e r a p i d l y d i e d down and p e r s i s t e n t a c t i v i t y c o n t i n u e d sometimes f o r s i x hours a f t e r c u t t i n g t h e n e r v e . T h i s a c t i v i t y had a f r e q u e n c y range o f l e s s than one i m p u l s e p e r second t o a maximum of 30. The f r e q u e n c y v a r i e d w i t h t h e f i s h and t h e l a t e r a l l i n e organ t h e ne r v e was i n n e r v a t i n g . I t was thought t h a t t h i s a c t i v i t y might o r i g i n a t e f r o m e i t h e r a v i s c e r a l e f f e r e n t nervous s u p p l y t o b l o o d v e s s e l s , s o m a t i c e f f e r e n t s u p p l y t o mu s c l e s , s e n s o r y e f f e r e n t s u p p l y t o l a t e r a l l i n e o r g a n s , o r c o l l a t e r a l a f f e r e n t n e r v e f i b e r s from a f f e r e n t s e n s o r y n e r v e s from t h e l a t e r a l l i n e o r g a n s . The c l o s e p r o x i m i t y o f n e r v e f i b e r s f r om t h e - 61 -TABLE V I I I . Impulses r e c o r d e d from p r o x i m a l end o f c u t n e r v e o r i g i n a l l y i n n e r v a t i n g l a t e r a l l i n e organ n9 ( F i g u r e 6.) s. . The c a n a l s were s t i m u l a t e d by w a t e r j e t from a s y r i n g e . Time f r o m S t a r t , D u r a t i o n No. o f L a t e r a l L i n e B e g i n n i n g o f and end o f Impulses C a n a l E xperiment S t i m u l u s P e r Second S t i m u l a t e d Seconds A 0 10 8 12 12 11 N a s a l 16 7 C a n a l 20 f 6 24 9 B 0 r 15 4 13 S u b - O r b i t a l 8 \ 1 16 C a n a l 16 15 C 0 1 [ 9 4 6 Trunk 20 f 5 C a n a l 28 9 D 0 7 16 7 Hyomandibulai 20 7 C a n a l 28 4 36 f 6 - 61a -D i a g r a m a t i c r e p r e s e n t a t i o n o f the r e s u l t s presented, i n T a b l e V I I I . A, B, C and D r e p r e s e n t t h e r e s u l t o f s t i m u l a t i n g d i f f e r e n t l a t e r a l l i n e c a n a l s by w a t e r j e t , and r e c o r d i n g from t h e e f f e r e n t n erve s u p p l y i n g l a t e r a l l i n e organ n9. A n a s a l c a n a l B s u b - o r b i t a l c a n a l C t r u n k c a n a l D h yomandibular c a n a l TIIUIF CFrnwns TIME, SECONDS - 61b -F i g u r e 8 A B i p o l a r r e c o r d i n g s o f a c t i o n p o t e n t i a l s f r o m a f i n e b ranch o f the ramus m a n d i b u l a r i s V i n n e r v a t i n g the muscle a d d u c t o r m a n d i b u l a r 3. B B i p o l a r r e c o r d i n g s o f a c t i o n p o t e n t i a l s from n e r v e Y o f t h e ramus b u c c a l i s f a c i a l i s . 01 SEC. - 62 -f a c i a l and trigeminal roots i n the o r b i t was the predicating factor i n making these assumptions. In two subsequent experiments a f i s h was prepared as previously described and bipolar s i l v e r stimulating electrodes were slipped under nerve Y i n one case, and nerve Z i n the other. These nerves were stimulated by D.C. and square wave pulses over a wide range of frequency from 1 per second to 1,000 per second and a duration of 0.1 micro-second to 1 millisecond, with a voltage range, at the beginning of the experiments of 0.001 v o l t to 10 v o l t s at the end. At the same time as the stimulation, the blood vessels i n the proximity of the o r b i t were observed to see i f they changed in diameter, and muscles i n and surrounding the o r b i t were observed to see i f they twitched in response to stimulation. No change i n diameter of the blood vessels, or twitching of the muscles was observed. In one further experiment a f i n e branch of the mandibullar branch of the vagus nerve of a goldfish was dissected free. Weak D.C. e l e c t r i c a l stimulation of t h i s resulted i n the contraction of the adductor mandibular 3 muscle. Bipolar s i l v e r recording electrodes were slipped under t h i s nerve and i t was then cut d i s t a l l y . The record from t h i s nerve (Figure 8 a ) was very regular and c l e a r l y p a l s a t i l e , unlike the c h a r a c t e r i s t i c a l l y i r r e g u l a r discharge from the f i n e nerve branches which apparently innervate the l a t e r a l l i n e organs (Figure 8 b ) . - 63 -TABLE IX. Impulses r e c o r d e d from i p s i l a t e r a l p r o x i m a l end o f c u t nerve s u p p l y i n g l a t e r a l l i n e organ n7 ( F i g u r e 6), s t i m u l a t e c o n t r a -l a t e r a l s i d e o f head w i t h v i b r a t i n g a i r b u b b l e s . Time from B e g i n n i n g o f D u r a t i o n No. o f Experiment o f Impulses Seconds S t i m u l u s P e r Second E 0 0 30 10 s e e s . 10 60 2 90 10 s e e s . 9 F 0 0 30 10 s e e s . 5 60 2 90 10 s e e s . 4 G 0 9 30 10 s e e s . 9 60 2 90 10 s e e s . 10 H 0 8 30 10 s e e s . 0 60 7 90 10 s e e s . 3 I 0 2 30 10 s e e s . 6 60 2 90 10 s e e s . 2 J 0 4 30 10 s e e s . 5 60 4 90 10 s e e s . 8 - 63a -D i a g r a m a t i c r e p r e s e n t a t i o n o f t h e r e s u l t s p r e s e n t e d i n T a b l e I X . E, F, G, H, I and J r e p r e s e n t a c o n s e c u t i v e s e r i e s o f r e c o r d i n g s t e n minutes a p a r t o b t a i n e d f rom t h e e f f e r e n t n e r v e s u p p l y i n g l a t e r a l l i n e o r g a n n7 d u r i n g t h e s t i m u l a t i o n o f t h e c o n t r a l a t e r a l s i d e o f t h e head w i t h a i r b u b b l e s . 3 0 6 0 9 0 TIME, SECONDS 3 0 6 0 90 TIME, SECONDS IMPULSES PER SECOND TIME, SECONDS 3 0 6 0 9 0 TIME, SECONDS 2 -O I 1 1 ' 3 0 6 0 9 0 TIME, SECONDS - 64 -I t was c o n c l u d e d t h a t t h e d i s c h a r g e o r i g i n a t e d e i t h e r f r om e f f e r e n t f i b e r s t o t h e l a t e r a l l i n e organs o r from c o l l a t e r a l s from a f f e r e n t f i b e r s s u p p l y i n g t h e s e o r g a n s . F i n e f i b e r s i n n e r v a t i n g s i n g l e l a t e r a l l i n e organs were exposed i n 3 f i s h i n 3 c o n s e c u t i v e e x p e r i m e n t s and b i p o l a r r e c o r d i n g e l e c t r o d e s were p l a c e d under them. R e c o r d -i n g s were made from f i b e r s i n n e r v a t i n g l a t e r a l l i n e organs Ng,N 7,N9, and N 1 4 ( F i g u r e 6 ) . These f i b e r s were c u t d i s t a l l y and r e c o r d e d from p r o x i m a l l y . The e f f e c t o f s t i m u l a t i n g i p s i l a t e r a l l a t e r a l l i n e c a n a l s , by w a t e r j e t s f r om a f i n e s y r i n g e , o r from t o u c h by a f i n e b r u s h , on the d i s c h a r g e from t h e p r o x i m a l ends o f t h e s e n e r v e s was o b s e r v e d . Each l a t e r a l l i n e c a n a l was s t i m u l a t e d i n d i v i d u a l l y by c o n c e n t r a t i n g t h e s t i m u l u s o v e r t h e a r e a of t h e c a n a l . R e s u l t s f o r s t i m u l a t i o n (by w a t e r j e t ) o f t h e n a s a l c a n a l , t h e hyomandibular c a n a l , t h e main t r u n k c a n a l , and t h e c a n a l i n the f i r s t s u b - o r b i t a l bone on t h e d i s c h a r g e i n t h e n e r v e f i b e r s s u p p l y i n g t h e l a t e r a l l i n e o r g a n N 9 o f a s i n g l e f i s h , have been p r e s e n t e d i n t a b u l a r and g r a p h i c a l form i n T a b l e V I I I and graphs A, B, C and D r e s p e c t i v e l y . No r e l a t i o n s h i p c o u l d be drawn between the r a t e of d i s c h a r g e and t h e a p p l i c a t i o n of t h e s t i m u l u s . T h i s t e s t was a p p l i e d on f i f t e e n f i s h i n subsequent e x p e r i m e n t s w i t h t h e same r e s u l t , namely no i n c r e a s e , o r d e c r e a s e , i n d i s c h a r g e r a t e of t h e p r o x i m a l c u t end of t h e s e f i b e r s c o u l d be c o r r e l a t e d w i t h t h e . a p p l i c a t i o n o f a s t i m u l u s t o n e i g h b o u r i n g i p s i l a t e r a l c a n a l s . - 65 -I n a f u r t h e r s e r i e s o f e x p e r i m e n t s i n v o l v i n g f i v e f i s h , f i n e f i b e r s t o l a t e r a l l i n e o rgans N g , N ^ , N g , and. N - ^ were exposed and t h e f i b e r s c u t d i s t a l l y so t h a t d i s c h a r g e s , o r i g i n a t i n g i n t h e p r o x i m a l ends o f t h e s e f i b e r s , c o u l d be r e c o r d e d . C o n t r a l a t e r a l - l a t e r a l l i n e c a n a l s i n t h e f i s h t s head were s t i m u l a t e d , once e v e r y 30 seconds f o r p e r i o d s o f 10 seconds each, by a i r b u b b l e s w h i c h were r e l e a s e d at a r a t e o f 2 p e r second f r o m a 3 mm. d i a m e t e r t u b e , c o n n e c t e d t o a compressed a i r s o u r c e . The tube was p l a c e d c l o s e to t h e s i d e o f t h e head o p p o s i t e t o t h a t b e i n g r e c o r d e d from, and i n such a manner t h a t t h e a i r b u b b l e brushed th e s i d e of t h e f i s h e s head as t h e y ascended to t h e s u r f a c e . T a b l e IX l i s t s a s e r i e s o f d i s c h a r g e r a t e s o b t a i n e d f rom t h e p r o x i m a l c u t end o f t h e n e r v e s u p p l y i n g l a t e r a l l i n e organ n 7 of a s i n g l e f i s h d u r i n g s t i m u l a t i o n , o f c o n t r a l a t e r a l - l a t e r a l l i n e c a n a l s by a i r b u b b l e s . These r e s u l t s have been r e p r e s e n t e d g r a p h i c a l l y i n graphs E,F,G,H,I and J , and o n l y i n graphs E and F i s t h e r e any c o r r e l a t i o n between d i s c h a r g e r a t e and s t i m u l u s , where t h e r e i s an i n c r e a s e i n d i s c h a r g e r a t e d u r i n g s t i m u l u s . T h i s i n c r e a s e i n d i s c h a r g e r a t e was f o u n d t o be c o r r e l a t e d w i t h movement o f t h e f i s h d u r i n g the s t i m u l u s , and no i n c r e a s e i n r a t e was n o t i c e d when the f i s h remained s t a t i o n a r y d u r i n g s t i m u l u s . - 66 -The N a t u r e o f t h e E f f e r e n t Nervous S u p p l y t o the L a t e r a l  L i n e Organs i n t h e L a t e r a l L i n e C a n a l s i n t h e Head o f t h e  G o l d f i s h . Nerves Y and Z o f t h e b u c c a l branch o f t h e f a c i a l n e r v e were exposed on one s i d e o f t h e head o f a f i s h . Hooked s i l v e r b i p o l a r e l e c t r o d e s were s l i p p e d under n e r v e Y and the spontaneous d i s c h a r g e from t h i s n e r v e bundle was r e c o r d e d f o r s e v e r a l m i n u t e s . The ne r v e bundle was s e v e r e d p r o x i m a l l y and t h e nervous d i s c h a r g e o f t h e d i s t a l p a r t o f t h e ne r v e was r e c o r d e d . I t was n o t i c e d t h a t t h e d i s c h a r g e r a t e o f t h i s p a r t o f t h e n e r v e was g r e a t e r t h a n t h a t p r e v i o u s l y r e c o r d e d from t h e n e r v e when i t had been i n t a c t . An i n c r e a s e i n d i s c h a r g e r a t e was not e x p e c t e d , because t h e d i s c h a r g e s r e c o r d e d i n b o t h n e r v e s Y and Z were thought to have been c o n t r i b u t e d t o by at l e a s t two s o u r c e s , namely a f f e r e n t n e r v e s from t h e l a t e r a l l i n e o r g a n s , and e f f e r e n t n e r v e s s u p p l y i n g t h e s e o r g a n s . E f f e c t i v e removal o f one of t h e s e s o u r c e s , t h e e f f e r e n t n e r v e s , by s e v e r i n g , i n t h i s p a r t i c u l a r i n s t a n c e n e r v e Y, p r o x i m a l l y , and r e c o r d i n g d i s t a l l y , was e x p e c t e d to d e c r e a s e t h e d i s c h a r g e r a t e . The i n c r e a s e i n d i s c h a r g e r a t e was not t r a n s i t o r y but was at a s u s t a i n e d l e v e l u n t i l t h e experiment was t e r m i n a t e d . T h i s experiment was s u b s e q u e n t l y r e p e a t e d , on ner v e Z of t h e same f i s h , and n e r v e s Y and Z o f t h r e e o t h e r f i s h e s , w i t h s i m i l a r r e s u l t s . R e s u l t s o f an experiment s i m i l a r t o t h e ones d e s c r i b e d above have been r e c o r d e d i n t a b u l a r and g r a p h i c a l form i n T a b l e X and Graph K r e s p e c t i v e l y . - 67 -TABLE X. The e f f e c t o f an a p p l i c a t i o n of s t r y c h n i n e t o t h e l a t e r a l l i n e o rgans o f t h e n a s a l c a n a l upon th e d i s c h a r g e o f the f i b e r s from t h e b u c c a l b r a n c h o f the f a c i a l n e r v e s u p p l y i n g t h e organs (Nerve Z, F i g u r e 6'),).. S t r y c h n i n e s u l p h a t e was a p p l i e d l o c a l l y t o t h e organs at a dose r a t e o f 0.5 mg. p e r k g . o f f i s h . Time i n M i n u t e s from b e g i n n i n g A p p l i c a t i o n S t a t e o f Impulses o f Experiment of S t r y c h n i n e Nerve Z p e r Second 0 40 1 33 2 35 3 4 < 5 6 a 63 7 8 p O 70 9 54 10 11 12 13 60 1 1 4 58 15 54 1 16 Ner 38 17 Ner 18 < ra 39 19 i Cut 37 20 i Cut 38 \ t - 67a -GRAPH 10; The d i a g r a m a t i c r e p r e s e n t a t i o n of r e s u l t s p r e s e n t e d i n T a b l e X. The e f f e c t o f an a p p l i c a t i o n o f s t r y c h n i n e t o t h e l a t e r a l l i n e o r g a n s of the n a s a l c a n a l upon the d i s c h a r g e o f t h e f i b e r s f r om t h e b u c c a l b r a n c h o f t h e f a c i a l n e r v e s i s u p p l y i n g t h e o r g a n s . (Nerve Z F i g u r e 6 ) . The a c t i v i t y l e v e l s o f d i s c h a r g e s r e c o r d e d f r om n e r v e Z have been drawn i n f o r normal c o n d i t i o n s , and a f t e r c u t t i n g t h e n e r v e and r e c o r d i n g d i s t a l l y . A sample of n e r v o u s a c t i v i t y d i s p l a y e d under the a p p r o p r i a t e a c t i v i t y l e v e l s . - 68 -TABLE X I . The e f f e c t o f c u t t i n g n e r v e Z ( F i g u r e 6-},) of the b u c c a l branch of t h e f a c i a l n e r v e , upon the d i s c h a r g e r e c o r d e d i n the dis^- :. ibal p a r t o f the f i b e r , and then a p p l y i n g s t r y c h n i n e l o c a l l y t o t h e organs i n n e r v a t e d by t h i s f i b e r i n t h e n a s a l c a n a l . S t r y c h n i n e s u l p h a t e a p p l i e d l o c a l l y t o r e c e p t o r s a t a dose r a t e o f 0.5 mg. p e r k g . f i s h . Time i n M i n u t e s from b e g i n n i n g o f E xperiment A p p l i c a t i o n o f S t r y c h n i n e S t a t e of Nerve Z Impulses p e r Second 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 o > CO M c+ H -<-i O p O t+ CS 0 O 4 <! Q O c 8 11 8 21 18 14 20 16 16 31 26 26 25 25 23 23 - 69 -GRAPH L D i a g r a m a t i c r e p r e s e n t a t i o n o f the r e s u l t s p r e s e n t e d i n T a b l e X I . The e f f e c t o f c u t t i n g n erve Z o f t h e b u c c a l b r a n c h of the f a c i a l n e r v e upon the d i s c h a r g e s r e c o r d e d i n t h e d i s t a l p a r t o f the f i b e r , and then a p p l y i n g s t r y c h n i n e l o c a l l y t o t h e organs i n n e r v a t e d by t h i s f i b e r i n the n a s a l c a n a l . The a c t i v i t y l e v e l s o f d i s c h a r g e s r e c o r d e d f r om n e r v e Z has been drawn i n f o r normal c o n d i t i o n s , a f t e r c u t t i n g and r e c o r d i n g d i s t a l l y and a f t e r t h e a p p l i c a t i o n o f s t r y c h n i n e . A sample of nervous a c t i v i t y i s d i s p l a y e d beneath the a p p r o p r i a t e a c t i v i t y l e v e l s . 32 2 8 2 4 4 2 0 16 8 \oo.y: loo./j.v, [_ O l SEC NORMAL NERVE CUT STRYCHNINE o 13 15 T I M E , M I N U T E S - 70 -One p o s s i b l e s o l u t i o n t o t h e p a r a d o x i c a l r e s u l t s o b t a i n e d i n t h e s e e x p e r i m e n t s was t h a t t h e e f f e r e n t nervous s u p p l y to t h e l a t e r a l l i n e o rgans had an i n h i b i t o r y a c t i o n on t h e g e n e r a t i o n o f n e r v e i m p u l s e s i n t h e a f f e r e n t n e r v e f i b e r . B e a r i n g i n mind the e l e c t r o n - m i c r o s c o p i c a l work o f F l o c k and W e r s a l l (1962), i n w h i c h t h e y showed the e x i s t e n c e ( t o t h e l a t e r a l l i n e organs o f L o t a v u l g a r i s ) o f two t y p e s of i n n e r v a t i o n , i n c l o s e p r o x i m i t y t o one a n o t h e r i t was c o n s i d e r e d p o s s i b l e t h a t t h e s i t e o f a c t i o n o f any i n h i b i t i o n , i f i t e x i s t e d , was a t the p o i n t where e f f e r e n t and a f f e r e n t n e r v e f i b e r s synapse on t h e h a i r c e l l . I n e x p e r i m e n t s p erformed s u c c e s s i v e l y on f o u r f i s h , n e r v e s Y and Z were exposed. Spontaneous nervous d i s c h a r g e f r o m n e r v e Z was r e c o r d e d f o r s e v e r a l m i n u t e s , and then s t r y c h n i n e s u l p h a t e , d i s s o l v e d i n s a l i n e , was i n j e c t e d i n t h e t i s s u e u n d e r l y i n g t h e neuromasts i n n e r v a t e d by t h e n erve b e i n g examined. The s t r y c h n i n e was a d m i n i s t e r e d a t a dose l e v e l o f 0.5 mg. p e r Kg. o f f i s h . A r a p i d , and s u s t a i n e d r i s e i n d i s c h a r g e r a t e was n o t i c e d , and t h i s c o u l d be o b s e r v e d f o r a p e r i o d o f 11 minutes (Graph L, T a b l e XI) o r f o r p e r i o d s up t o 1 hour i n o t h e r e x p e r i m e n t s . The n e r v e was s e v e r e d d i s t a l l y and r e c o r d i n g was c o n t i n u e d p r o x i m a l l y , w i t h t h e r e s u l t t h a t an immediate drop i n d i s c h a r g e r a t e was o b s e r v e d . T h i s d e c r e a s e d r a t e was m a i n t a i n e d w i t h o u t r e c o v e r y , a t a l e v e l s l i g h t l y above t h a t i n i t i a l l y r e c o r d e d i n t h e i n t a c t n e r v e , u n t i l t h e t e r m i n a t i o n of t h e e x p e r i m e n t . S i m i l a r r e s u l t s were o b t a i n e d f o r e x p e r i -ments performed on b o t h Z and Y f o r each of the f o u r f i s h . - 71 -A s e r i e s o f c o n t r o l e x p e r i m e n t s were performed on f o u r more f i s h . Spontaneous a c t i v i t y was r e c o r d e d i n t h e x i n t a c t n e r v e s Y and Z f o r s e v e r a l m i n u t e s . The n e r v e was c u t and t h e r e c o r d i n g c o n t i n u e d from t h e d i s t a l p a r t o f t h e n e r v e . An immediate r i s e i n d i s c h a r g e r a t e was ob s e r v e d (Graph L, T a b l e XI) and t h i s was a l l o w e d to c o n t i n u e at a s u s t a i n e d r a t e f o r a p e r i o d o f two and one h a l f minutes when an i n j e c t i o n of s t r y c h n i n e s u l p h a t e was a d m i n i s t e r e d t o the t i s s u e s beneath t h e neuromasts i n n e r v a t e d by nerve Z. No change i n d i s c h a r g e r a t e was o b s e r v e d as a r e s u l t o f the s t r y c h n i n e i n j e c t i o n . T h i s o b s e r v a t i o n h e l d t r u e f o r a l l r e m a i n i n g e x p e r i m e n t s performed on n e r v e s Y and Z o f t h e f o u r f i s h . - 72 -DISCUSSION E l e c t r o n - m i c r o s c o p i c a l e v i d e n c e p r e s e n t e d by F l o c k and W e r s a l l (1962) r e g a r d i n g t h e d o u b l e i n n e r v a t i o n t o t h e h a i r c e l l s o f t h e l a t e r a l l i n e organs o f L o t a v u l g a r i s , d i d not i n d i c a t e i f one of t h e s e n e r v e components was t r u l y e f f e r e n t o r p o s s i b l e r e c u r r e n t c o l l a t e r a l f i b e r s from a f f e r e n t n e r v e f i b e r s . I n the i n i t i a l i n v e s t i g a t i o n i n t h e s e e x p e r i -ments an a l l o w a n c e was made f o r t h e p o s s i b i l i t y t h a t t h e d i s c h a r g e r e c o r d e d f rom the p r o x i m a l end o f a s e v e r e d bundle of n e r v e s s u p p l y i n g a l a t e r a l l i n e o r g a n might be a n t i d r o m i c a f f e r e n t d i s c h a r g e s and not d i s c h a r g e s o f e f f e r e n t o r i g i n . Doubt as to t h e o r i g i n of the d i s c h a r g e was m i t i g a t e d by t h e r e s u l t s o f t h e s u c c e e d i n g e x p e r i m e n t s w h i c h i n d i c a t e d t h a t s t i m u l a t i o n o f s u r r o u n d i n g l a t e r a l l i n e o r g a n s , both c o n t r a -l a t e r a l and i p s i l a t e r a l , had no n o t i c e a b l e e f f e c t upon t h e d i s c h a r g e r a t e o f t h e p r o x i m a l p o r t i o n of t h e s e v e r e d n e r v e . S t i m u l a t i o n o f t h e s e a d j a c e n t neuromasts would presumably produce p o t e n t i a l s i n any e x i s t i n g c o n t r a l a t e r a l s to o t h e r neuromasts. No i n c r e a s e d a c t i v i t y was r e c o r d e d upon s t i m u -l a t i o n o f a d j a c e n t neuromasts and t h e r e f o r e i t seems p r o b a b l e t h a t t h e r e a r e no c o n t r a l a t e r a l a f f e r e n t s i n the l a t e r a l l i n e n e r v e . A c t i v i t y r e c o r d e d f r o m t h e p r o x i m a l ends of the c u t n e r v e s was from e f f e r e n t f i b e r s i n n e r v a t i n g t h e neuromast. R e c e n t l y Schmidt (1965) p r e s e n t e d e v i d e n c e f o r an e f f e r e n t nervous s u p p l y t o t h e l a t e r a l l i n e organs o f N e c t u r u s  maculosus and f o r a s i m i l a r s u p p l y t o t h e l a t e r a l l i n e organs o f a s i n g l e specimen of Rana p i p i e n s . Gorner (1966) has - 73 -p r e s e n t e d e v i d e n c e f o r an e f f e r e n t nervous s u p p l y t o t h e l a t e r a l l i n e organs o f Xenopus, but i n n e i t h e r c a s e i s t h e r e e v i d e n c e t h a t the a c t i v i t y r e c o r d e d was not a n t i d r o m i c a f f e r e n t a c t i v i t y , and on t h e s e grounds i t i s c o n s i d e r e d t h a t t h e i r e v i d e n c e remains i n c o n c l u s i v e on t h i s p o i n t . I n t h e second p a r t o f t h e experiment i t was found t h a t t h e d i s c h a r g e r a t e o f t h e d i s t a l p a r t o f t h e s e v e r e d n e r v e was g r e a t e r t h a n th e r a t e o f the i n t a c t n e r v e . From t h e s e r e s u l t s i t i s s u g g e s t e d t h a t the a c t i v i t y i n t h e e f f e r e n t f i b e r s t o t h e l a t e r a l l i n e organs might have an i n h i b i t o r y e f f e c t upon the a c t i v i t y o f t h e a f f e r e n t f i b e r s . Thus when th e n e r v e i s c u t i n h i b i t i o n o f t h e neuromast i s r e l e a s e d , and t h e r a t e o f d i s c h a r g e i n t h e a f f e r e n t f i b e r s i n c r e a s e s . S t r y c h n i n e i s w e l l known t o s y n a p t i c a l l y b l o c k p o s t - s y n a p t i c i n h i b i t o r y a c t i o n ( E c c l e s ( 1 9 6 4 ) ) . E c c l e s , F a t and K o k e t u (1954) employed s t r y c h n i n e s u l p h a t e t o s u p p r e s s e f f e r e n t a c t i v i t y i n t h e s p i n a l c o r d o f a c a t , and t h e y found t h a t a dose r a t e o f 0.03 mg. p e r Kg. o f c a t , w h i c h i s a s u b - c o n v u l s a n t dose, reduced the i n h i b i t o r y p o s t s y n a p t i c p o t e n t i a l s i n t h e s p i n a l c o r d n e r v e s by more th a n h a l f . E c c l e s (1964) n o t e d t h a t g r e a t e r doses would v i r t u a l l y e l i m i n a t e t h e i n h i b i t o r y p o s t s y n a p t i c p o t e n t i a l . I t was found by C u r t i s (1962) from i n t r a c e l l u l a r r e c o r d i n g s from s p i n a l neurones d u r i n g i o n t o p h o r e t i c i n j e c t -i o n s o f s t r y c h n i n e , t h a t t h e s t r y c h n i n e d i d not d e p r e s s th e a c t i v i t y o f t h e neurone b e i n g examined. From t h i s e v i d e n c e he s u g g e s t e d t h a t t h e e f f e c t o f s t r y c h n i n e was c o n f i n e d t o . - 74 -the r e g i o n o f t h e i n h i b i t o r y synapse. Galambos (1956), Fex (1962), and Desmedt (1962) used s t r y c h n i n e s u l p h a t e t o b l o c k the i n h i b i t o r y a c t i o n o f the o l i v o - c o c h l e a r bundle upon t h e g e n e r a t i o n of i m p u l s e s i n t h e a f f e r e n t n e r v e f i b e r s from c o c h l e a r h a i r c e l l s . The a c t i o n of s t r y c h n i n e upon t h e e f f e r e n t f i b e r s , and e f f e r e n t s y n a p s e s , o f t h e l a t e r a l l i n e organ h a i r c e l l s i s unknown. However, i t was thought t h a t i f t h e s e f i b e r s d i d i n h i b i t t h e g e n e r a t i o n o f i m p u l s e s i n a f f e r e n t f i b e r s i n n e r v a t i n g t h e l a t e r a l l i n e h a i r c e l l s , then i t would n o t be u n r e a s o n a b l e t o c o n s i d e r t h a t an a p p l i c a t i o n o f s t r y c h n i n e s u l p h a t e t o t h e r e g i o n o f t h e e f f e r e n t synapses would b l o c k t h i s i n h i b i t o r y a c t i o n . E x p e r i m e n t a l r e s u l t s i n d i c a t e d t h a t t h e a p p l i c a t i o n o f s t r y c h n i n e t o t h e base of t h e l a t e r a l l i n e o rgans i n c r e a s e d a f f e r e n t a c t i v i t y . C o n t r o l e x p e r i m e n t s performed a f t e r t h e s e e x p e r i m e n t s demonstrated t h a t t h e i n c r e a s e d a c t i v i t y a s s o c i a t e d w i t h t h e a p p l i c a t i o n o f s t r y c h n i n e was not a r e s u l t o f an e x c i t a t o r y e f f e c t o f s t r y c h n i n e on the e f f e r e n t n e r v e s and t h a t s t r y c h n i n e had no o b s e r v a b l e e f f e c t upon t h e d i s c h a r g e r a t e o f t h e a f f e r e n t f i b e r s . T h i s i n d i r e c t e v i d e n c e s u p p o r t e d t h e c o n c l u s i o n t h a t t h e e f f e r e n t f i b e r s were i n h i b i t o r y . Schmidt (1966) and Gorner (1966) were u n a b l e t o show any e f f e c t o f t h e a c t i v i t y o f the e f f e r e n t n e r v e f i b e r s upon the a c t i v i t y i n a f f e r e n t n e r v e f i b e r s i n n e r v a t i n g t h e l a t e r a l l i n e systems t h e y were i n v e s t i g a t i n g . Gorner c o n c l u d e d t h a t h i s r e s u l t s i n d i c a t e d an independence o f e f f e r e n t nervous a c t i v i t y f r o m a f f e r e n t nervous a c t i v i t y i n t h e nerve f i b e r s i n n e r v a t i n g t h e neuromasts o f Xenopus, and c o n s i d e r e d t h a t - 75 -a n o t h e r approach t o t h e problem was r e q u i r e d . S i n c e t h e b l o c k i n g a c t i o n o f s t r y c h n i n e i s t o compete p o s t s y n a p t i c a l l y w i t h t h e i n h i b i t o r y t r a n s m i t t e r f o r r e c e p t o r s i t e s ( E c c l e s 1964) th e n t h e i n h i b i t o r y t r a n s m i t t e r a c t s upon t h e p o s t s y n a p t i c membrane i n some way. There i s an i n c r e a s i n g amount o f e v i d e n c e , summarized by E c c l e s (1964) w h i c h i n d i c a t e s t h a t t h e r o l e of t h e i n h i b i t o r y t r a n s m i t t e r i s t o m a i n t a i n the p o s t s y n a p t i c membrane a t r e s t i n g p o t e n t i a l o r s l i g h t l y below i t . E c c l e s has s u g g e s t e d f u r t h e r , s i n c e a l l t h e p o s t s y n a p t i c i n h i b i t o r y e f f e c t s t h a t have been i n v e s t i g a t e d i n t h e s p i n a l c o r d o f t h e c a t a r e b l o c k e d by s t r y c h n i n e , t h a t t h e y a r e a l l caused by the same t r a n s m i t t e r s u b s t a n c e , and t h e drugs w h i c h are b e l i e v e d t o a c t by c o m p e t i t i v e o c c u p a t i o n o f t h e r e c e p t o r s i t e s would be s t e r i c a l l y r e l a t e d t o t h e i n h i b i t o r y t r a n s -m i t t e r . He s u g g e s t e d a l s o from e v i d e n c e p r e s e n t e d by Galambos, Fex, and Desmedt, who used s t r y c h n i n e t o b l o c k the i n h i b i t o r y e f f e c t o f t h e o l i v o - c o c h l e a r b u n d l e upon the a f f e r e n t c o c h l e a r n e r v e a c t i v i t y , t h a t t h e same i n h i b i t o r y t r a n s m i t t e r i s r e s p o n s i b l e f o r i n h i b i t i o n i n t h i s c a s e . T h i s argument c o u l d , t h e r e f o r e , a l s o be extended to the a c t i o n of e f f e r e n t f i b e r s on t h e l a t e r a l l i n e o r g a n s . However, t o d a t e no t r a n s m i t t e r s u b s t a n c e has been i s o l a t e d o r i d e n t i f i e d a t t h e synapses o f any h a i r c e l l system (Tanaka and K a t s u k i 1966). , - 76 -I n o c o n c l u s i o n i t would appear t h a t t h e neuromasts of the l a t e r a l l i n e system are i n n e r v a t e d by e f f e r e n t n erve f i b e r s . The a c t i o n o f t h e s e n e r v e s i s t o i n h i b i t a c t i v i t y i n t h e a f f e r e n t f i b e r s from t h e same neuromast. There appears t o be no c o n t r a l a t e r a l o r i p s i l a t e r a l i n t e r a c t i o n between neuromasts v i a t h i s e f f e r e n t n e r v e s u p p l y . The a c t i o n of t h e l a t e r a l l i n e e f f e r e n t s appears t o be v e r y s i m i l a r t o t h a t o f the e f f e r e n t f i b e r s i n n e r v a t i n g the h a i r c e l l s i n t h e c o c h l e a r o f t h e c a t . - 77 -NEUROPHYSIOLOGY:PART 2 INTRODUCTION Desmedt (1962) s u g g e s t e d a p s y c h o p h y s i o l o g i c a l r o l e f o r t h e o l i v o - c o c h l e a r e f f e r e n t nervous s u p p l y t o t h e c o c h l e a r h a i r c e l l s . One s u g g e s t i o n was t h a t t h e a b i l i t y t o n e u r o p h y s i o l o g i c a l l y s u p p r e s s some sounds and enhance t h e p e r c e p t i o n o f o t h e r s might be under c o r t i c a l c o n t r o l . P r e v i o u s b e h a v i o u r e x p e r i m e n t s have shown t h a t f i s h a r e a b l e t o l o c a l i s e a sound s o u r c e a g a i n s t background n o i s e . I n t h i s c a s e t h e background n o i s e encompasses e v e r y a c o u s t i c phenomena e x c e p t t h o s e emanating from the sound s o u r c e . Even t h e f i s h ' s body movements a r e , under t h e s e c o n d i t i o n s , counted as background n o i s e . The p r e v i o u s e x p e r i m e n t s i n d i c a t e d t h a t t h e a c t i v i t y of the e f f e r e n t f i b e r s t o the l a t e r a l l i n e o r g a n s of t h e g o l d f i s h remained u n a f f e c t e d by t h e s t i m u l a t i o n o f t h e o t h e r l a t e r a l l i n e o rgans o f t h e same f i s h by t o u c h , w a t e r j e t , and a i r b u b b l e s . These s t i m u l i would n o t o n l y s t i m u l a t e t h e l a t e r a l l i n e o r g a n s , but would a l s o a f f e c t t h e o t h e r organs w h i c h a re a c o u s t i c a l l y r e c e p t i v e , such as t h e e a r s and t h e t o u c h r e c e p t o r s . I t would appear, t h e r e f o r e , t h a t t h e a c t i v i t y c a r r i e d i n t h e e f f e r e n t f i b e r s t o the neuromasts does n ot o r i g i n a t e i n n e i g h b o u r i n g neuromasts o r i n o t h e r a c o u s t i c a l l y r e c e p t i v e systems. What then i s t h e o r i g i n o f t h e e f f e r e n t a c t i v i t y t o t h e l a t e r a l l i n e o r g a n s , and how, i f a t a l l , i s i t r e l a t e d t o t h e l e v e l o f background n o i s e ? - 78 -Knowing t h a t t h e e f f e r e n t f i b e r s do not appear to be a f f e c t e d by t h e s t i m u l a t i o n o f s u r r o u n d i n g a c o u s t i c a l l y s e n s i t i v e systems, i t was d e c i d e d t o i n v e s t i g a t e t h e e f f e c t o f c e r t a i n t y p e s o f n o i s e caused by body movements upon th e l a t e r a l l i n e o r g a n e f f e r e n t s . - 7 9 -EXPERIMENTAL The g e n e r a l e x p e r i m e n t a l p r o c e d u r e s and ap p a r a t u s used i n t h e s e e x p e r i m e n t s have a l r e a d y been d e s c r i b e d i n the p r e v i o u s s e c t i o n . However, i n t h i s s e r i e s o f e x p e r i m e n t s the o p e r c u l a r movements of t h e f i s h were m o n i t o r e d . A s m a l l h o l e was made near t h e o u t e r margin o f t h e operculum and a f i n e s t e e l hook i n s e r t e d i n t h i s h o l e . A t h r e a d s e c u r e d t h e hook t o t h e arm o f a m e c h a n o e e l e c t r i c t r a n s d u c e r mounted above t h e operculum. A s i n g l e c o r e d , s c r e e n e d c a b l e connected t h e t r a n s d u c e r to the i n p u t o f a n o t h e r 122 p r e - a m p l i f i e r w h i c h was now used as a s i n g l e s i d e d p r e - a m p l i f i e r w i t h one o f . : ' . i t s . . " d i f f e r e n t i a l i n p u t s c o n n e c t e d t o ground. T h i s s i g n a l was then f e d i n t o t h e o t h e r c h a n n e l o f t h e tap e r e c o r d e r and t h e o s c i l l o s c o p e . I n o r d e r to i n v e s t i g a t e t h e e f f e c t o f i n t r a m u s c u l a r i n j e c t i o n s o f t u b o c u r a r i n e c h l o r i d e upon t h e d i s c h a r g e r a t e o f t h e l a t e r a l l i n e o r g an e f f e r e n t n e r v e s , t u b e r c u r a r i n e c h l o r i d e d i s s o l v e d i n s a l i n e was i n j e c t e d d i r e c t l y i n t o t h e mu s c l e s . The t u b e r c u r a r i n e c h l o r i d e was a d m i n i s t e r e d t o the f i s h a t a dose r a t e o f 0.1 mg. p e r 100 gms. o f f i s h t h r o u g h a s y r i n g e f i t t e d w i t h a 23 gauge hyp e r d e r m i c n e e d l e . - 80 -RESULTS The E f f e c t o f O p e r c u l a r Movements Upon the Rate of D i s c h a r g e  f r om the L a t e r a l - L i n e E f f e r e n t N e r v e s . Ten g o l d f i s h were used i n t h e s e e x p e r i m e n t s and i n no case c o u l d any r e l a t i o n s h i p be drawn between e i t h e r t h e o p e r c u l a r movement r a t e o r t h e a m p l i t u d e o f movement, w i t h e f f e r e n t d i s c h a r g e s r e c o r d e d from Y and Z o f t h e b u c c a l b ranch o f t h e f a c i a l n e r v e ( F i g u r e 6 ) . The o p e r c u l a r movements were r e c o r d e d on t h e upper t r a c e o f t h e o s c i l l o s c o p e , and the e f f e r e n t d i s c h a r g e s were s i m u l t a n e o u s l y r e c o r d e d on t h e lower t r a c e ( F i g u r e 9a and 9 b ) . The l a c k of r e l a t i o n s h i p between o p e r c u l a r movement and e f f e r e n t d i s c h a r g e h e l d whether th e f i s h was i n the w a t e r o r out of i t . T h u s , i t would seem t h a t t h e e f f e r e n t s p l a y no p a r t i n s u p p r e s s i n g n o i s e produced by t h e b r e a t h i n g movements. The neuromasts o f t h e head must t h e r e f o r e r e c o r d t h e w a t e r d i s p l a c e m e n t s a s s o c i a t e d w i t h i t s own b r e a t h i n g movements. I t i s o f c o u r s e p o s s i b l e t h a t t h i s i n f o r m a t i o n i s r e j e c t e d at a more: c e n t r a l l e v e l i n t h e nervous system. The E f f e c t o f t h e G e n e r a l L e v e l o f M u s c u l a r A c t i v i t y , and the  I n t r a m u s c u l a r I n j e c t i o n o f T u b e r c u r a r i n e C h l o r i d e on the  D i s c h a r g e Rate from th e L a t e r a l L i n e Qrgan E f f e r e n t N e r v e s . Three g o l d f i s h were used i n t h i s e xperiment and t h e n e r v e s Y and Z o f t h e b u c c a l branch of the f a c i a l n e rve - 81 -F i g u r e 9 A The s i m u l t a n e o u s r e c o r d i n g o f o p e r c u l a r movements, upper t r a c e , and b i p o l a r e l e c t r o d e r e c o r d i n g s o f a c t i o n p o t e n t i a l s i n e f f e r e n t f i b e r s o f n e r v e Y, when t h e f i s h was h e l d o u t o f w a t e r . B The s i m u l t a n e o u s r e c o r d i n g s o f o p e r c u l a r movement, upper t r a c e , and b i p o l a r e l e c t r o d e r e c o r d i n g s o f a c t i o n p o t e n t i a l s i n e f f e r e n t f i b e r s of n e r v e Y when the f i s h was submersed i n w a t e r . OPERCULAR MOVEMENTS ACTION POTENTIALS IOO jJV.j I SEC. IOOjJ.V.| 0-2 SEC. so;jy. I 0-2 SEC. 50 JJV. L I SEC. IOO JJ.V L 0-2 SEC B - 82 -TABLE XI Ii; The a p p l i c a t i o n o f t u b e r c u r a r i n e c h l o r i d e i n t r a m u s c u l a r l y t o the o p e r c u l a r muscles of g o l d f i s h , and the changes i n e f f e r e n t a c t i v i t y a s s o c i a t e d w i t h t h e c h a n g i n g m u s c u l a r s t a t e of t h e f i s h when r e c o r d e d from n e r v e Z ( F i g u r e 6 ) . Time from b e g i n n i n g o f experiment (minutes) D u r a t i o n and Type of M u s c u l a r A c t i v i t y A p p l i c a t i o n o f T u b e r c u r a r i n e Impulses p e r Second 0 R e s p i r a t i o n 19 1 ti 20 2 ti 25 3 it 18 4 it 18 5 ti 15 6 tt A p p l i c a t i o n of 14 7 R e s p i r a t i o n Ceased C u r a r i n e 7 8 ti ti 5 9 it it 3 10 ti it 3 11 ti ti 6 12 tt it 7 13 S t r u g g l i n g 11 7 14 ti it 27 15 it ti 31 16 tt ii 24 17 tt ti 25 18 ti it f 25 - 82 a -GRAPH M Diagrammatic r e p r e s e n t a t i o n of t h e r e s u l t s p r e s e n t e d i n T a b l e X I I . The a p p l i c a t i o n o f t u b e r c u r a r i n e c h l o r i d e i n t r a m u s c u l a r l y t o the o p e r c u l a r muscles o f g o l d f i s h , and the changes i n e f f e r e n t a c t i v i t y a s s o c i a t e d w i t h t h e c h a n g i n g m u s c u l a r s t a t e o f t h e f i s h when r e c o r d e d from n e r v e Z. The a c t i v i t y l e v e l s o f d i s c h a r g e s r e c o r d e d from n e r v e Z has been drawn i n f o r normal c o n d i t i o n s d u r i n g r e g u l a r r e s p i r a t o r y movement, a f t e r t h e a p p l i c a t i o n of t u b e r c u r a r i n e and subsequent c e s s a t i o n o f m u s c u l a r a c t i v i t y , and d u r i n g v i o l e n t m u s c u l a r a c t i v i t y . RESPIRATORY MOVEMENT MOVEMENT CEASED STRUGGLING MOVEMENT TUBOCURINE CHLORIDE 8 10 12 14 16 18 TIME, MINUTES - 83 -were d i s c l o s e d f o r b i p o l a r recording.. The operculum was co n n e c t e d t o t h e arm o f t h e m e c h a n o - e l e c t r i c t r a n s d u c e r by a t h r e a d , and t h e movement of t h e operculum, and t h e r e c o r d i n g s o f e f f e r e n t a c t i v i t y f r o m n e r v e s Y and Z were d i s p l a y e d on the o s c i l l o s c o p e . The o p e r c u l a r movements and t h e e f f e r e n t a c t i v i t y f rom n e r v e Z were o b s e r v e d f o r s i x minutes i n one p a r t i c u l a r p r e p a r a t i o n ( T a b l e X I I and Graph M). The r a t e o f d i s c h a r g e from t h e e f f e r e n t s was o b s e r v e d to v a r y between 15 and 25 i m p u l s e s p e r second. At t h e end o f 6 minutes t u b e r c u r a r i n e c h l o r i d e was i n j e c t e d i n t r a m u s c u l a r l y i n t o the o p e r c u l a r muscles at a dose r a t e o f 0.1 mg. o f t u b e r c u r a r i n e p e r 100 gms. o f f i s h ( D . J . R a n d a l l and G. S h e l t o n 1963) and one minute l a t e r t h e o p e r c u l a r movements were o b s e r v e d t o c e a s e . The e f f e r e n t d i s c h a r g e r a t e f e l l t o 7 i m p u l s e s p e r second, and s u b s e q u e n t l y w i t h i n t h r e e m i n u t e s , t o t h r e e i m p u l s e s p e r second. T h i r t e e n minutes a f t e r t h e s t a r t o f the e x p e r i m e n t , the f i s h began t o show mu s c u l a r a c t i v i t y . A l t h o u g h i t s r e s p i r a t o r y movement appeared t o be weak o r n o n - e x i s t e n t , the f i s h , r a i s e d i t s d o r s a l f i n , extended i t s p e l v i c and p e c t o r a l f i n s and attempted to escape from t h e clamp. S i m u l t a n e o u s l y w i t h t h e appearance of i n c r e a s e d muscular movement t h e e f f e r e n t a c t i v i t y r o s e from a d i s c h a r g e r a t e o f 7 i m p u l s e s p e r second t o 25 and s u b s e q u e n t l y to a maximum o f 31 i m p u l s e s p e r second. T h i s f e l l e v e n t u a l l y t o 24 p e r se c o n d . U n f o r t u n a t e l y , due t o v i o l e n t s t r u g g l i n g on t h e p a r t - 84 -of t h e f i s h i t broke l o o s e f rom t h e clamp 18 minutes from the b e g i n n i n g of the experiment and the experiment was t e r m i n a t e d . I n t h e o t h e r two e x p e r i m e n t s t h e e f f e r e n t f i b e r s responded i n t h e same manner t o t h e a p p l i c a t i o n o f c u r a r i n e . However, i t was not p o s s i b l e t o produce any m u s c u l a r a c t i v i t y f r o m t h e a n i m a l a f t e r t h e c u r a r e i n j e c t i o n . - 85 -DISCUSSION That t h e d i s c h a r g e from the e f f e r e n t f i b e r s i n n e r v a t i n g the l a t e r a l l i n e organs d i d not change i n res p o n s e t o the o p e r c u l a r movements, i n d i c a t e d t h a t e i t h e r t h e r e was no d i r e c t c e n t r a l pathway between t h e r e s p i r a t o r y c e n t r e and t h e l a t e r a l l i n e n u c l e i , o r i f t h e r e was the ti m e c o n s t a n t o f t h e t r a n s f e r o f i n f o r m a t i o n from the r e s p i r a t o r y c e n t r e t o t h e l a t e r a l l i n e n u c l e i was too slow f o r t h e l a t e r a l l i n e n u c l e i t o re s p o n d . T u b e r c u r a r i n e c h l o r i d e , when i n j e c t e d i n t r a v e n t r i -c u l a r l y i n t o the b r a i n s o f c a t s produces acute c o n v u l s i o n s , and when i n j e c t e d i n t r a v e n o u s l y produces motor p a r a l y s i s o r n e u r o m u s c u l a r b l o c k ( F e l d b e r g 1963). T u b e r c u r a r i n e c h l o r i d e i s a l a r g e m o l e c u l e , and t h e r e i s l i t t l e exchange, i f any, o f t h i s d r u g between t h e b l o o d s t r e a m and t h e b r a i n a c r o s s t h e b l o o d - b r a i n b a r r i e r i n c a t s . F e l d b e r g p o i n t s o u t , t h a t i f a b s o r b t i o n o f i n t r a v e n t r i c u l a r t u b e r c u r a r i n e were t o o c c u r , the e n s u i n g neuromuscular b l o c k would mask the c e n t r a l l y i n d u c e d c o n v u l s i o n s . That t h i s does not happen does not mean t h a t no t u b e r c u r a r i n e escapes t h e b r a i n , but t h a t amounts absorbed by the b l o o d s t r e a m a r e too s m a l l t o b l o c k motor e n d p l a t e s . I t i s b e l i e v e d t h a t the r e s u l t s o b s e r v e d i n t h i s e x periment were not as a r e s u l t o f t h e a c t i o n o f t u b e r c u r a r i n e on the f i s h e s c e n t r a l nervous system, because t h e l e v e l s o f t u b e r c u r a r i n e used were so s m a l l . There was i n s u f f i c i e n t - 86 -t u b e r c u r a r i n e i n j e c t e d i n t r a m u s c u l a r l y to c o m p l e t e l y b l o c k a l l t h e motor end p l a t e s , and s i n c e i t i s b e l i e v e d t h a t t u b e r c u r a r i n e a c t i v e l y competes w i t h the t r a n s m i t t e r s u b s t a n c e at t h e n e u r o m u s c u l a r j u n c t i o n ( D e l C a s t i l l o and K a t z 1957) then most of t h e i n t r a m u s c u l a r l y i n j e c t e d t u b e r -c u r a r i n e would have bound i t s e l f to r e c e p t o r s i t e s on p o s t s y n a p t i c motor end p l a t e membranes, and l i t t l e would have passe d i n t o t h e b l o o d s t r e a m . I f t h e q u a n t i t y o f t u b e r c u r a r i n e i n j e c t e d i n t r a m u s c u l a r l y had been v e r y l a r g e , then any e n t e r i n g t h e b l o o d s t r e a m and p e n e t r a t i n g t o t h e b r a i n would have had no n o t i c e a b l e c o n v u l s i v e e f f e c t due t o t h e p a r a l y s e d s t a t e of t h e f i s h . I n c r e a s e d m u s c u l a r a c t i v i t y i s a s o u r c e o f s e n s o r y i n p u t t o t h e b r a i n t h r o u g h th e a c t i o n of p r o p r i o c e p t o r s s i t u a t e d i n the m u s c l e s . T h i s i n c r e a s e d a f f e r e n t a c t i v i t y i s a l s o an i n d i c a t i o n o f an i n c r e a s e i n e f f e r e n t a c t i v i t y , as the b r a i n c o n t r o l s o t h e r p r o p r i o c e p t o r s and motor axons t o a n t a g o n i s t i c m u s c l e s . A s s o c i a t e d w i t h i n c r e a s e d m u s c u l a r movement i s a r e q u i r e m e n t f o r i n c r e a s e d s e n s o r y awareness. F o r example, i n l o c o m o t i o n th e speed o f l o c o m o t i o n of t h e f i s h i s p a r t i a l l y dependent upon the f i s h e s a b i l i t y to r a p i d l y o r i e n t a t e i t s e l f . I t seems f e a s i b l e , t h e r e f o r e , t o r e c o r d a r i s e i n e f f e r e n t a c t i v i t y t o t h e l a t e r a l l i n e organs d u r i n g i n c r e a s e d m u s c u l a r a c t i v i t y s i n c e l a t e r a l l i n e organs are c o n s i d e r e d t o be at l e a s t p a r t i a l l y concerned w i t h t h e o r i e n t a t i o n o f t h e f i s h . C o n v e r s e l y i t i s not s u r p r i s i n g t o o b s e r v e a d e c r e a s e i n e f f e r e n t a c t i v i t y d u r i n g muscular i n a c t i v a t i o n - 87 -by t h e a p p l i c a t i o n o f a p a r a l y z i n g d r u g such as t u b e r c u r a r i n e c h l o r i d e . The e f f e c t o f t h e a p p a r e n t l y t o t a l b l a n k e t i n h i b i t o r y a c t i o n o f the e f f e r e n t s on the l a t e r a l l i n e organs by the i n c r e a s e d m u s c u l a r a c t i v i t y cannot be d i s c u s s e d a t t h i s s t a g e , but w i l l be d i s c u s s e d l a t e r on i n t h e l i g h t o f e v i d e n c e o b t a i n e d from o t h e r f i e l d s . - 88 -HYDRODYNAMICAL INVESTIGATION To I n v e s t i g a t e Changes i n Hydrodynamic F i e l d Around t h e  Heads o f S t a t i o n a r y and Swimming G o l d f i s h caused by  R e s p i r a t o r y Movements o f t h e F i s h . INTRODUCTION A p a r t from b e i n g a p o s s i b l e s o u r c e o f n o i s e t o the f i s h , r e s p i r a t o r y movements may a l s o change t h e hydrodynamic f i e l d around the f i s h , a l s o c h a n g i n g the s t i m u l u s f i e l d around t h e l a t e r a l l i n e o r g a n s , on t h e head o f t h e f i s h . An i n v e s t i g a t i o n o f t h e hydrodynamic f i e l d around th e heads of swimming and s t a t i o n a r y g o l d f i s h was p r o p o s e d . I t was i n t e n d e d t o i n v e s t i g a t e any changes w h i c h may t a k e p l a c e i n t h e hydrodynamic f i e l d d u r i n g r e s p i r a t i o n , and to see i f t h e r e was any i n d i c a t i o n t h a t f i s h c o u l d use t h e s e changes as an a i d to d i r e c t i o n a l l y l o c a t i n g o b j e c t s and t h e near f i e l d d i s p l a c e m e n t s o f sound s o u r c e s i n the wat e r s u r r o u n d i n g t h e f i s h . - 89 -F i g u r e 10 A S c h e m a t i c a l diagram o f t h e o p t i c s o f the' system used to o b s e r v e b i r e f r i n g e n c e i n t h e H e c t o r b e n t o n i t e s o l u t i o n . B The arrangement of t h e f l u i d p o l a r o s c o p e used i n t h i s e x p e r i m e n t . C The arrangement o f the o p t i c a l system used i n t h e e x p e r i m e n t . VERTICAL CIRCULAR POLARIZATION POLARIZATION O LIGHT SOURCE VIBRATIONS IN DIRECTION OF PRINCIPAL STRESSES CIRCULAR POLARIZATION ASSUMED HORIZONTAL POLARIZATION COMPONANTS DISPLACED POLARIZER >4 WAVE PLATE FLOW SECTION ANALYZER WAVE PLATE INLET-12* LONG FLOW TANK CONTAINING l%HECTORITE SOLUTION GLASS FIBRE SCREENS' 7 OUTLET PUMP TYGON TUBING COOLING COIL -VARIABLE TRANSFORMER B 3 5 M M C A M E R A WITH T E L E P H O T O L E N S L O A D E D WITH P L U S X F I L M V E R T I C A L S U P P O R T C O N D E N S I N G L E N S O P T I C A L AXIS T W O Q U A R T E R WAVE P L A T E A N D A N A L Y Z E R — T A N K P O L A R I Z E R A N D F IRST Q U A R T E R W A V E P L A T E C O L L U M A T I N G L E N S E S HEAT A N D C O L O U R FILTERS T O P R O D U C E S O D I U M B A N D O N L Y 150 W A T T V A P O U R L A M P - 90 -EXPERIMENTAL Theory of the f l u i d P o l a r o s c o p e The t h e o r y f o r t h e f l u i d p o l a r o s c o p e i s the same as t h a t f o r p h o t o - e l a s t i c s t r e s s a n a l y s i s i n the s o l i d p o l a r i s c o p e , i n t h a t s t r e s s d i s t r i b u t i o n can be d e t e r m i n e d by f i n d i n g t h e magnitude and d i r e c t i o n of two p r i n c i p a l s t r e s s e s i n a two d i m e n s i o n a l model. T h i s i s done by p a s s i n g p o l a r i s e d l i g h t t h r o u g h th e s o l i d two d i m e n s i o n a l model and l o o k i n g f o r two t y p e s of l i n e s as t h e y appear at t h e a n a l y s i n g s c r e e n . The i s o c h r o m a t i c ( a s i n g l e c o l o u r , o n l y when a monochromatic l i g h t s o u r c e i s used) g i v e s t h e magnitude o f t h e p r i n c i p a l s t r e s s e s , and t h e i s o c l i n i c s g i v e t h e i n c l i n a t i o n o f t h e p r i n c i p a l s t r e s s e s . The, model must be c o n s t r u c t e d o f a m a t e r i a l w h i c h becomes b i r e f r i n g e n t when s t r e s s e d . The p o l a r i s e d l i g h t when p a s s i n g t h r o u g h the m a t e r i a l i s s p l i t i n t o two components each o f w h i c h v i b r a t e i n t h e d i r e c t i o n o f a p r i n c i p a l s t r e s s , and each moves th r o u g h the m a t e r i a l a t d i f f e r e n t speeds. I n t h e f l u i d p o l a r o s c o p e H e c t o r B e n t o n i t e i s t h e o p t i c a l l y a c t i v e m a t e r i a l . I n t h e system s e t out below ( F i g u r e 10a) , q u a r t e r wave p l a t e s were used t o e l i m i n a t e t h e i s o c l i n i c s so t h a t t h e i s o c h r o m a t i c l i n e s c o u l d be more e a s i l y o b s e r v e d . i l- The q u a r t e r wave p l a t e s s p l i t l i g h t e n t e r i n g them i n t o two components v i b r a t i n g at 90° t o one a n o t h e r and l e a v i n g t h e q u a r t e r wave p l a t e s 90° out o f phase. T h i s - 91 -produces a combined c o n t i n u a l l y r o t a t i n g , o r c i r c u l a r l y p o l a r i s e d , l i g h t . When the c i r c u l a r l y p o l a r i s e d l i g h t p a s s e s through t h e f l o w s e c t i o n no i s o c l i n i c s w i l l be formed because th e l i g h t i s none d i r e c t i o n a l , a n d , t h e r e f o r e , n o l i g h t w i l l be p assed s t r a i g h t t h r o u g h and a l l t h e l i g h t r e a c h i n g t h e second q u a r t e r wave p l a t e w i l l have components i n the d i r e c t i o n o f t h e p r i n c i p a l s t r e s s e s . The l i g h t l e a v i n g t h e second q u a r t e r wave p l a t e and e n t e r i n g t h e a n a l y s e r i s a g a i n i n two components, 90° t o each o t h e r and out o f phase, t h e s e w i l l i n t e r a c t w i t h each o t h e r i f t h e y are out o f phase and produce i s o c h r o m a t i c l i n e s . The degree t o w h i c h th e components are out o f phase depends upon the amount of b i r e f r i n g e n c e e x h i b i t e d by t h e s o l u t i o n , and t h i s depends on t h e s i z e o f t h e p r i n c i p a l s t r e s s e s w i t h i n i t . I n a f l u i d the p r i n c i p a l s t r e s s e s s e t up are the e f f e c t i v e s h e e r s t r e s s due t o v e l o c i t y d i f f e r e n t i a l s a c r o s s the d i r e c t i o n o f f l o w . A p p a r a t u s The P r e p a r a t i o n o f t h e B i r e f r i n g e n t S o l u t i o n . H e c t o r B e n t o n i t e . The p r e p a r a t i o n o f t h e s o l u t i o n was f o l l o w e d from d i r e c t i o n s g i v e n by t h e B a r o i d D i v i s i o n o f t h e N a t i o n a l Lead Company who are t h e m a n u f a c t u r e r s of H e c t o r B e n t o n i t e (McPherson and Nece 1950). H e c t o r i t e i s found w i t h 50% c a l c i t e and d o l o m i t e - 92 -as a m o n t m o r i l l o m i t e c l a y , and t h e c a l c i t e and d o l o m i t e must be removed from the h e c t o r i t e b e f o r e use. To remove t h e c a l c i t e and d o l o m i t e t h e c l a y was d i s p e r s e d a t (3%) i n w a t e r c o n t a i n i n g 0.01% t e t r a sodium pyrophosphate w i t h a h i g h speed s t i r r e r i n a l a r g e g l a s s tank f o r about two h o u r s . T h i s was then a l l o w e d t o s t a n d o v e r n i g h t u n t i l a l l o f t h e c a l c i t e had s e t t l e d o u t . The s u p e r n a t e n t s u s p e n s i o n was th e n d e c a n t e d o f f and c e n t r i f u g e d to remove p a r t i c l e s c o a r s e r t h a n a p p r o x i m a t e l y 0.5 m i c r o n s . The s o l i d c o n t e n t i n t h e s o l u t i o n was a d j u s t e d t o 1% b e f o r e use. The P o l a r o s c o p e The p o l a r o s c o p e used i n t h i s e x periment was a l o n g , s h a l l o w p l e x i g l a s s tank ( F i g u r e 10b) t h r o u g h w h i c h h e c t o n i t e s o l u t i o n was c i r c u l a t e d by an e l e c t r i c a l l y d r i v e n , v a r i a b l e speed, r o t a r y pump. At each end o f t h e tank a s e r i e s o f f i n e g l a s s f i b e r meshes were p l a c e d i n a s t a g g e r e d assembly, i . e . d i f f e r e n t d i s t a n c e s s e p a r a t i n g each mesh s c r e e n , t o break up t u r b u l e n t f l o w as the w a t e r e n t e r e d and l e f t t he t a n k . I n one s e t of t h e e x p e r i m e n t s t h e o p t i c a l a x i s of t h e p o l a r o s c o p e ( F i g u r e 10c) was s e t so t h a t i t was i n a v e r t i c a l p l a n e t h r o u g h t h e t a n k , and i n the o t h e r s e t o f e x p e r i m e n t s i t was a r r a n g e d t o be i n a h o r i z o n t a l a x i s t h r o u g h t h e w a l l s o f t h e t a n k . - 93 -E x p e r i m e n t a l P r o c e d u r e The f i s h was p l a c e d i n the tank and t h e w a t e r v e l o c i t y t h r o u g h t h e tank i n c r e a s e d u n t i l t h e f i s h had t o swim s t r o n g l y t o m a i n t a i n p o s i t i o n i n t h e t a n k . The camera was then f o c u s e d on t h e f i s h . The l i g h t i n g i n t h e tank however was poor, and a compromise was made between th e a p e r t u r e s i z e and t h e s h u t t e r t i m i n g w h i c h was not o p t i m a l . I n a n o t h e r experiment the f l o w was reduced t o z e r o , and hydrodynamic f i e l d around t h e f i s h was o b s e r v e d under s t a t i o n a r y c o n d i t i o n s . - 9 4 -RESULTS The hydrodynamic f i e l d about t h e heads o f seven g o l d f i s h 3 - 4 " l o n g was s t u d i e d i n both s i d e and top e l e v a t i o n s . The o p e r c u l a r movements o f s t a t i o n a r y f i s h , d u r i n g r e s p i r a t i o n caused an a r e a o f b i r e f r i n g e n c e t o be formed i n the v i c i n i t y of t h e operculum and t h i s was c o n s i d e r e d t o be caused by t h e d i s p l a c e m e n t o f w a t e r . Under c l o s e s c r u t i n y . ; i t c o u l d be seen t h a t d u r i n g e l e v a t i o n of t h e operculum, w a t e r was b o t h pushed away (damming e f f e c t ) and pushed f o r w a r d s ( s h e a r i n g e f f e c t ) a l o n g t h e s u r f a c e o f t h e operculum. U n f o r t u n a t e l y no s u c c e s s f u l photographs were t a k e n o f t h i s m otion due to the e x t r e m e l y poor l i g h t i n g c o n d i t i o n s . D u r i n g d e p r e s s i o n o f t h e operculum w a t e r was drawn back i n a v o r t e x caused by t h i s movement. In t h e s u c c e s s i v e s e r i e s of e x p e r i m e n t s t h e g o l d f i s h were made t o swim a g a i n s t a c u r r e n t . The swimming movements of t h e f i s h caused v o r t i c e s t o be g e n e r a t e d a l o n g t h e i r b o d i e s . However,the v o r t i c e s were n e v e r n o t i c e d t o ext e n d f a r t h e r f o r w a r d s t h a n t h e t r a i l i n g edge o f the o p e r c u l a r ( F i g u r e 1 1a). When the f i s h swam w i t h t h e i r mouths s h u t , a bow wave was g e n e r a t e d about t h e i r heads ( F i g u r e l i b ) however t h i s was seen to be reduced when t h e f i b h swam w i t h t h e i r mouths open ( F i g u r e 11c) as i n d i c a t e d by the d e c r e a s e d a r e a of b i r e f r i n g e n c e s u r r o u n d i n g t h e head o f the f i s h . A l s o a t the commencement o f t h e mouth open phase o f r e s p i r a t i o n a s m a l l a r e a of b i r e f r i n g e n c e c o u l d be d e t e c t e d ahead o f t h e - 9 5 -F i g u r e 11 Drawings made from photographs t a k e n o f f i s h swimming through t h e H e c t o r b e n t o n i t e s o l u t i o n . A S i d e view o f g o l d f i s h showing l a c k o f t u r b u l e n c e ahead o f t h e p o s t e r i o r b o r d e r o f the operculum d u r i n g swimming. B E n l a r g e d d o r s a l view o f t h e head of a g o l d f i s h swimming w i t h i t s mouth c l o s e d . C E n l a r g e d d o r s a l view o f t h e head of a g o l d f i s h swimming w i t h i t s mouth open. An a r e a o f n e g a t i v e p r e s s u r e has been s t i p p l e d ahead o f t h e f i s h . - 96 -f i s h . T h i s was thought t o i n d i c a t e t h e n e g a t i v e p r e s s u r e caused by i n h a l a t i o n d u r i n g r e s p i r a t i o n . - 97 -DISCUSSION The s h e a r i n g e f f e c t caused by t h e movement of w a t e r a l o n g t h e moving operculum o f a s t a t i o n a r y f i s h c o u l d be c o n s i d e r e d as a s o u r c e o f n o i s e but r e s p i r a t o r movements i n r e s t i n g g o l d f i s h are u s u a l l y q u i t e s l o w , and i t i s u n l i k e l y t h a t t h i s would reduce t h e s e n s i t i v i t y of t h e l a t e r a l l i n e organs o f t h e f i s h t o a g r e a t e x t e n t . From a n o t h e r p o i n t of view t h e f i s h c o u l d d e t e c t changes i n t h e hydrodynamic f i e l d caused by t h e o p e r c u l a r movements as a means t o d e t e c t s t a t i o n a r y o b j e c t s c l o s e t o t h e f i s h . Swimming f i s h a l t e r n a t e between two t y p e s o f e f f e c t i v e f l o w shapes d u r i n g t h e i r r e s p i r a t o r y sequence; namely between b l u f f b o d i e s and s t r e a m l i n e d b o d i e s . F i s h p h y s i c a l l y r esemble b l u f f b o d i e s when t h e i r mouths are s h u t , p u s h i n g w a t e r ahead o f them and s e t t i n g up a r e g i o n o f p o s i t i v e p r e s s u r e i n t h e w a t e r ahead o f them. With t h e i r mouths open, and i n h a l i n g w a t e r and e x p e l l i n g i t a g a i n from p o i n t s under t h e t r a i l i n g edges of t h e o p e r c u l a r , f i s h behave as s t r e a m l i n e d b o d i e s . T h i s i s because w a t e r ahead o f the f i s h w h i c h i s not a b l e t o escape r a p i d l y enough o v e r t h e s u r f a c e o f t h e f i s h d u r i n g swimming i s sucked away by t h e * r e s p i r a t o r y pump, t h u s , a v o i d i n g any b u i l d up o f p o s i t i v e p r e s s u r e , and i n c r e a s e d w a t e r r e s i s t a n c e ahead o f t h e f i s h . One consequence o f t h i s s t r e a m l i n i n g i s t h a t f i s h swimming w i t h t h e i r mouths open r e q u i r e l e s s energy f o r - 98 -l o c o m o t i o n than f i s h w i t h t h e i r mouths c l o s e d . F a s t swimming f i s h such as the m a c k e r e l and t h e t u n a are known t o c o n t i n u a l l y swim w i t h t h e i r mouths open. With t h e i r mouths c l o s e d f i s h c o u l d d e t e c t the p o s i t i o n s o f s t a t i o n a r y o r v i b r a t i n g o b j e c t s ahead of them by m easuring changes i n c o n f i g u r a t i o n o f t h e bow wave caused by d i s p l a c e m e n t s s e t up by t h e v i b r a t i n g o b j e c t , on t h e one hand, o r i n c r e a s e d r e s i s t a n c e t o motion of t h e f i s h by v i r t u e o f t h e p r e s e n c e of t h e r o d , on t h e o t h e r . T h i s p o s s i b i l i t y has a l r e a d y been mentioned by D i j g r a a f (1963) and W a l t e r s (1966) but t h e y d i d not mention t h a t t h i s bow wave changed c o n f i g u r a t i o n c o n t i n u o u s l y d u r i n g r e s p i r a t i o n . I t i s a l s o q u i t e p o s s i b l e t h a t t h e l a t e r a l l i n e organs would be p o t e n t i a l l y more r e c e p t i v e to d i s p l a c e m e n t when the f i s h have t h e i r mouths c l o s e d . T h i s i s because a l a r g e v e l o c i t y g r a d i e n t e x i s t s a c r o s s t h e bow wave so t h a t t h e v e l o c i t y of t h e water l a y e r a d j a c e n t t o t h e f i s h e s s u r f a c e would be c l o s e t o z e r o when measured w i t h r e f e r e n c e to t h e f i s h e s v e l o c i t y . Thus, the l a t e r a l l i n e organ c u p u l a e would not be d e f l e c t e d by w a t e r d i s p l a c e d by t h e f i s h e s swimming mo t i o n , and s o , p o t e n t i a l l y would be c a p a b l e o f r e s p o n d i n g to g r e a t e r w a t e r d i s p l a c e m e n t changes than c u p u l a e a l r e a d y d i s p l a c e d . The w a t e r l a y e r a d j a c e n t to the s u r f a c e o f the s t r e a m l i n e d f i s h , because o f t h e l a r g e v e l o c i t y g r a d i e n t o f t h i s l a y e r , would be t r a v e l l i n g at a v e l o c i t y s i m i l a r t o t h a t o f t h e f i s h e s swimming v e l o c i t y when measured w i t h - 99 -r e s p e c t t o t h e f i s h . L a t e r a l l i n e organs on t h e f i s h e s head under t h e s e c o n d i t i o n s would then be d e f l e c t e d an amount p r o p o r t i o n a l to t h e v e l o c i t y o f swimming. I t seems q u i t e p o s s i b l e , t h e r e f o r e , t h a t d u r i n g the r e s p i r a t o r y c y c l e a f i s h may a l t e r n a t e l y d e t e c t d i s p l a c e m e n t s i n the w a t e r around i t , and measure i t s own swimming v e l o c i t y . The v o r t i c e s g e n e r a t e d down the s i d e o f t h e f i s h e s t r u n k c o u l d be used by the f i s h f o r e s t i m a t i n g i t s swimming speed w i t h r e s p e c t t o t h e w a t e r s u r r o u n d i n g i t . The v o r t i c e s would cause the l a t e r a l l i n e o rgans t o be d e f l e c t e d as t h e y passed down the body, and the q u i c k e r t h e f i s h swims the f a s t e r t h e v o r t i c e s would r o l l down the s i d e o f t h e f i s h . K u i p e r (1966) gave a t h e o r y f o r t h e g e n e r a t i o n o f v o r t i c e s , h i s main c o n c l u s i o n s were t h a t v o r t i c e s were formed d u r i n g swimming motion (he had not seen, o r heard o f e v i d e n c e , of t h e i r f o r m a t i o n ) and t h a t t h e y always a r i s e from the same p o i n t on t h e f i s h d u r i n g swimming, and t h a t t h e y accompanied the f i s h as i t swam. Rosen (1966) s u p p o r t e d K u i p e r ' s t h e o r y by e x p l a i n i n g t h a t he had t a k e n photographs o f a f i s h swimming a c r o s s a w a t e r - m i l k i n t e r p h a s e , and t h a t he had n o t i c e d t h e f o r m a t i o n o f v o r t i c e s on the m i l k s u r f a c e w h i c h accompanied t h e f i s h as he swam. He d i d not produce h i s photographs t o s u p p o r t h i s s t a t e m e n t . K u i p e r ' s t h e o r y and Rosen's s t a t e m e n t s are not i n agreement w i t h Newton's Law of a c t i o n and r e a c t i o n , and my f i n d i n g s do not agree w i t h Rosen's. The v o r t i c e s g e n e r a t e d by swimming movements i n g o l d f i s h are l e f t b ehind by t h e - 100 -g o l d f i s h , s i n c e t h e y do, a f t e r a l l , r e p r e s e n t w a t e r d i s p l a c e -ments, and t h e r e i s no e v i d e n c e t o show t h a t t h e y are g e n e r a t e d from any p a r t i c u l a r p o i n t s on t h e s u r f a c e o f the f i s h . - 101 -GENERAL DISCUSSION Pumphrey (1950) c l e a r l y d e f i n e d what he c o n s i d e r e d h e a r i n g , the a c t o f h e a r i n g , and a sound s o u r c e t o be:-"The p r i m i t i v e f u n c t i o n of h e a r i n g i s t h e l o c a t i o n o f moving o b j e c t s n o t i n c o n t a c t w i t h t h e a n i m a l . An a n i m a l h e a r s when i t behaves as i f i t has l o c a t e d a moving o b j e c t , a sound s o u r c e , n o t i n c o n t a c t w i t h i t . Sound can be d e f i n e d as any m e c h a n i c a l d i s t u r b a n c e w h i c h i s p o t e n t i a l l y r e f e r a b l e t o an e x t e r n a l and l o c a l i s e d s o u r c e " . B e a r i n g Pumphrey's d e f i n i t i o n s i n mind, i t appears t h a t t h e f i s h i n t h e b e h a v i o u r e x p e r i m e n t s d e s c r i b e d p r e v i o u s l y were r e s p o n d i n g t o sound s o u r c e s , were l o c a l i s i n g them, and c o n s e q u e n t l y h e a r i n g them. Pumphrey d i d not s t a t e what r e f e r e n c e p o i n t s he was c o n s i d e r i n g when he d e f i n e d t h a t an a n i m a l h e a r s when i t l o c a t e s a moving o b j e c t , but presumably he was c o n s i d e r i n g movement o f t h e o b j e c t w i t h r e s p e c t t o th e a n i m a l . I n w h i c h case t h e f i s h i n t h e s e e x p e r i m e n t s can be s a i d t o be d e t e c t i n g t h e p o s i t i o n o f t h e s t a t i o n a r y r o d by r e s p o n d i n g t o a c o u s t i c a l s t i m u l a t i o n brought about by t h e i n t e r a c t i o n o f t h e f i s h e s bow wave w i t h t h e r o d , and a v o i d i n g i t . The b e h a v i o u r e x p e r i m e n t s i n d i c a t e d t h a t the l a t e r a l l i n e organs were d i r e c t i o n a l l y s e n s i t i v e t o t h e v i b r a t i n g r o d , and t o d i s p l a c e m e n t s r e s u l t i n g f r om i n t e r a c t i o n o f t h e f i s h ' s bow wave w i t h t h e s t a t i o n a r y r o d s . The p o i n t of view t h a t t h e f i s h ' s l a t e r a l l i n e organs are both d i r e c t i o n a l l y - 102 -and d i s p l a c e m e n t s e n s i t i v e has been p r e v i o u s l y put f o r w a r d i n t h e o r e t i c a l terms by B e r g e i j k (1963), and from e x p e r i m e n t a l e v i d e n c e d e r i v e d from i n v e s t i g a t i o n s o f t h e l a t e r a l l i n e m i c r o p h o n i c s o f F u n d u l a s by H a r r i s and B e r g e i j k (1962). C o n s i d e r i n g H a r r i s and B e r g e i j k * s r e s u l t s , Pumphrey*s d e f i n i -t i o n s and t h e b e h a v i o u r e x p e r i m e n t s p r e s e n t e d h e r e , i t i s c o n c l u d e d t h a t t h e l a t e r a l l i n e organs a r e i m p l i c a t e d as organs o f s h o r t range h e a r i n g . D i j k g r a a f (1963) i s s t r o n g l y opposed to t h e view t h a t t h e l a t e r a l l i n e f u n c t i o n s as a s h o r t range h e a r i n g system. He c o n s i d e r s t h a t f i s h do not use t h e i r l a t e r a l l i n e systems f o r l o c a t i n g o r even d e t e c t i n g sound s o u r c e s . In 1935, Von F r i s c h and D i j k g r a a f made the o b s e r v a t i o n , from e x p e r i m e n t s upon minnows, t h a t t h e i r b e h a v i o u r c o n t r a d i c t e d t h e i d e a o f sound as a d i r e c t i o n a l s t i m u l u s , and a l t h o u g h f i s h h e a r d v e r y w e l l , l o c a t i o n o f the sound s o u r c e w i t h t h e a i d of p r o p a g a t e d waves seemed beyond t h e i r c a p a b i l i t i e s . Von F r i s c h and S t e t t e r (1932) used b l i n d e d P h o x i n u s and c o n d i t i o n e d t h e s e a n i m a l s t o f e e d t o t h e s o u n d i n g o f a t u n i n g f o r k . They t h e n , b i l a t e r a l l y , removed t h e s a c c u l u s and l a g e n a from t h e s e f i s h and demonstrated t h a t t h e f i s h f a i l e d t o respond t o f r e q u e n c i e s above 150 c p s . , but s t i l l responded t o f r e q u e n c i e s below t h i s . E l i m i n a t i o n o f the l a t e r a l l i n e o rgans s t i l l d i d not d i s t u r b t h e r e s p o n s e s o f t h e f i s h . - 103 -P a r k e r (1902) used u n c o n d i t i o n e d Fundulus i n h i s e x p e r i m e n t s , w h i c h c l e a r l y r e a c t e d t o t u n i n g f o r k s o f 100-128 c p s . r e s p e c t i v e l y . Complete e l i m i n a t i o n of t h e l a t e r a l l i n e organs d i d not d i m i n i s h t h e s e n s i t i v i t y . But when b o t h t h e l a b y r i n t h s were removed, o r t h e e i g h t h n e r v e had been c u t b i l a t e r a l l y , the r e a c t i o n s were a b o l i s h e d , a l t h o u g h t h e l a t e r a l l i n e s were l e f t i n t a c t . These e x p e r i m e n t s and s e v e r a l o t h e r s quoted by D i j k g r a a f f a i l e d t o r e c o g n i s e t h e d i v i s i o n of sound energy i n t o two forms, t h e ne a r f i e l d d i s p l a c e m e n t e f f e c t and t h e f a r f i e l d p r e s s u r e e f f e c t . There i s i n d i c a t i o n t h a t Von F r i s c h and D i j k g r a a f (1935) were unaware o f the p r e s e n c e of near f i e l d d i s p l a c e m e n t s a s s o c i a t e d w i t h a sound s o u r c e . A l s o t h e i r concept o f sound b e i n g a d i r e c t i o n a l s t i m u l u s i s f a l l a c i o u s , because a t the t i m e t h a t remark was made, t h e y c o n s i d e r e d sound t o c o n s i s t o f p r o p a g a t e d p r e s s u r e waves, which a re not v e c t o r q u a n t i t i e s . The same comments may a l s o be l e v e l l e d at P a r k e s (1902) e x p e r i m e n t s and F r i s c h and S t e t t e r (1932). N e i t h e r group i n d i c a t e d i f t h e re s p o n s e t h e y e l i c i t e d from the f i s h by s o u n d i n g a t u n i n g f o r k was d i r e c t i o n a l . S i n c e i t i s c o n s i d e r e d t h a t one of the c r i t e r i a o f sound p e r c e p t i o n i s d i r e c t i o n a l i t y , F r i s c h and S t e t t e r ' s and P a r k e s * e x p e r i m e n t s must remain i n c o n c l u s i v e . Thus t h e e v i d e n c e p r e s e n t e d by D i j k g r a a f t o s u p p o r t h i s argument a g a i n s t t h e l a t e r a l l i n e organs b e i n g s e n s i t i v e - 104 -t o low f r e q u e n c y sound i s thought to be i n c o n c l u s i v e from one p o i n t o f v i e w , namely, t h a t t h e a c o u s t i c e v i d e n c e upon which i t i s based i s i l l d e f i n e d . A n o t h e r s e c t i o n o f D i j k g r a a f s (1963) r e v i e w r e c o g n i s e s t h e s i g n i f i c a n c e o f t h e n e a r f i e l d e f f e c t produced by a sound s o u r c e , but does n o t c o n s i d e r t h e p e r c e p t i o n o f i t t o c o n s t i t u t e h e a r i n g . He b e l i e v e s t h a t t h e l a t e r a l l i n e organs are c u r r e n t d e t e c t o r s r e s p o n d i n g t o a m p l i t u d e , d i r e c t i o n and e x t e n t o f w a t e r d i s p l a c e m e n t s a p p l i e d as s p a t i a l and t e m p o r a l p a t t e r n s t o t h e s u r f a c e o f the a n i m a l . He t h u s does not c o n s i d e r the need t o d e s i g n a t e t h e l a t e r a l l i n e s ystem as a v i b r a t i o n r e c e p t o r o r even as a s h o r t range a u d i t o r y r e c e p t o r (Pumphrey 1950) s i n c e t h e adequate s t i m u l i a re n e i t h e r e s s e n t i a l l y v i b r a t o r y nor do t h e y i n c l u d e sound i n the normal meaning of p r o p a g a t e d , r h y t h m i c a l l y , r e p e a t e d p r e s s u r e waves. In t h e f i r s t p l a c e , t h e r e i s n e u r o p h y s i o l o g i c a l e v i d e n c e a v a i l a b l e t o show t h a t b o t h c u r r e n t s t i m u l a t i o n (Sand 1937) and v i b r a t i o n a l s t i m u l a t i o n ( K a t s u k i 1951, 1952) are adequate s t i m u l i t o t h e l a t e r a l l i n e o r g a n s . There i s however, no e v i d e n c e a v a i l a b l e a t p r e s e n t t o i n d i c a t e t h a t e i t h e r o f t h e s e s t i m u l i are b i o l o g i c a l l y adequate. The hydrodynamic e x p e r i m e n t s i n d i c a t e d t h a t t h e s u r f a c e s o f t h e f i s h may o n l y r a r e l y be exposed t o d i r e c t w a t e r c u r r e n t s . The w a t e r , d i s p l a c e d as a r e s u l t o f l o c o m o t i o n , down the s i d e s o f t h e g o l d f i s h i n t h e s e e x p e r i m e n t s was i n t h e f o r m of v o r t i c e s . Even r e s p i r a t o r y c u r r e n t s , caused by the - 105 -pumping of w a t e r from t h e b u c c a l c a v i t y o f t h e f i s h caused v o r t i c e s o r t u r b u l a n c e . The e f f e c t o f t h e passage of v o r t i c e s o r t u r b u l a n t w a t e r passed a l a t e r a l l i n e o r g an would be t o o s c i l l a t e i t i r r e g u l a r l y and a t low f r e q u e n c y . D i j k g r a a f s c oncept o f t h e normal meaning of sound as b e i n g p r o p a g a t e d , r h y t h m i c a l l y , r e p e a t e d p r e s s u r e waves i s an o v e r r - s i m p l i f i c a t i o n . Sound i s r a r e l y r h y t h m i c , and under D i j k g r a a f s c o n c e p t , speed and e x p l o s i v e sounds, f o r example, would be, o u t s i d e t h e normal meaning o f sound. S e c o n d l y h i s c o n c e p t o f sound as b e i n g p r o p a g a t e d p r e s s u r e waves i s s u b j e c t i v e . T e r r e s t i a l a n i m a l s , i n p a r t i c u l a r , may use the p r o p e r t i e s o f t h e f a r f i e l d p r e s s u r e waves t o d e t e c t and l o c a l i s e a sound s o u r c e , but t h i s i s no j u s t i f i c a t i o n f o r c o n s i d e r i n g an organ w h i c h responds t o the n e a r f i e l d d i s p l a c e m e n t s as not b e i n g an organ o f h e a r i n g . I t i s c o n c l u d e d t h a t arguments w h i c h have been p r e s e n t e d t o e x c l u d e the l a t e r a l l i n e organs as organs o f h e a r i n g are b a s i c a l l y u n a c c e p t a b l e on t h e grounds t h a t t h e y f a i l t o r e c o g n i s e the near f i e l d e f f e c t as an a c o u s t i c a l s t i m u l u s . On t h e s e grounds i t i s thought t h a t t h e r e a r e , at p r e s e n t , no j u s t i f i a b l e r e a s o n s f o r not a c c e p t i n g the l a t e r a l l i n e organs as organs o f s h o r t range h e a r i n g . The a c o u s t i c f i e l d t o w h i c h the l a t e r a l l i n e organs respond d i s p l a y s g r e a t e r c o n t r a s t than t h e f i e l d t o w h i c h the e a r s r e s p o n d . T h i s i s because t h e d i s p l a c e m e n t s o f t h e n e a r f i e l d e f f e c t o f sound s o u r c e s a t t e n u a t e v e r y r a p i d l y - 106 -i w i t h d i s t a n c e from t h e sound s o u r c e , u n l i k e t h e s e l f p r o p a g a t i n g p r e s s u r e waves of t h e f a r f i e l d . T h i s d i s c r e e t n e s s o f t h e n e a r f i e l d would t e n d t o reduce t h e chance o f i n t e r -a c t i o n between th e near f i e l d s o f a d j a c e n t sound s o u r c e s , and thus p r e s e n t s a s h a r p e r more c o n t r a s t i n g f i e l d t o the l a t e r a l l i n e o r g a n s , than t h e a c o u s t i c f i e l d o f t h e a s s o c i a t e d p r e s s u r e waves would do t o the e a r s . A n o t h e r f e a t u r e w h i c h c o n t r i b u t e s t o s i m p l i f y i n g i n t e r p r e t a t i o n o f t h e s e n s o r y f i e l d o f the l a t e r a l l i n e o rgans i s t h e d e f i n i t e p o l a r i z a t i o n of t h e d i s p l a c e m e n t s . The l a t e r a l l i n e organs have a p o l a r i s e d s e n s i t i v i t y t o w a t e r d i s p l a c e m e n t s , w h i c h makes them s e n s i t i v e o n l y t o d i s p l a c e m e n t s a l o n g one a x i s . T h i s g i v e s f i s h a f a c i l i t y f o r a n a l y s i n g t h e d i r e c t i o n o f t h e s e d i s p l a c e m e n t s w i t h o u t t h e n e c e s s i t y of r e s o r t i n g t o c o m p l i c a t e d c e n t r a l mechanisms, a p o i n t w h i c h has p r e v i o u s l y been made. Thus f i s h would be a b l e , i f t h e y used t h i s f a c i l i t y t o reduce t h e d i s p l a c e m e n t s i n t h e a c o u s t i c f i e l d of t h e i r l a t e r a l l i n e systems i n t o d i r e c t i o n a l components. There i s b e h a v i o u r a l e v i d e n c e , w h i c h has been p r e v i o u s l y d i s c u s s e d , t o i l l u s t r a t e t h e a b i l i t y o f f i s h t o d i f f e r e n t i a t e between v e r t i c a l and h o r i z o n t a l d i s p l a c e m e n t s . A l t h o u g h t h e a c o u s t i c f i e l d of t h e d i s p l a c e m e n t e f f e c t s f rom sound s o u r c e s p r e s e n t s a c o n t r a s t i n g s t i m u l u s t o t h e l a t e r a l l i n e o r g a n s , the problems o f background n o i s e i s o m n i p r e s e n t . L a r g e amorphous d i s p l a c e m e n t s from w a t e r c u r r e n t s , s u r f a c e waves, and g e n e r a l t u r b u l e n c e c o n t r i b u t e t o t h e major s o u r c e o f n o i s e t o t h e s e n s o r y f i e l d o f t h e - 107 -l a t e r a l l i n e organs and, i t i s c o n s i d e r e d n e c e s s a r y t o propose the e x i s t e n c e o f a mechanism w h i c h s u p p r e s s e s t h i s e f f e c t . B e h a v i o u r a l e v i d e n c e i s a v a i l a b l e t o demonstrate t h a t f i s h a r e a b l e t o d e t e c t d i s p l a c e m e n t s from a sound s o u r c e a g a i n s t d i s p l a c e m e n t s of g r e a t e r magnitude c o n t r i b u t e d by background n o i s e . The c o c h l e a r and t h e l a t e r a l l i n e system a re b o t h c o n f r o n t e d w i t h a common a c o u s t i c a l problem, namely t h e s e l e c t i o n of s p e c i f i c sounds from a background o f n o i s e . B o t h t h e l a t e r a l l i n e , from r e s u l t s o b t a i n e d i n t h e p r e v i o u s l y d e s c r i b e d b e h a v i o u r e x p e r i m e n t s , and the e a r s (Bekesy 1960) appear t o be c a p a b l e o f overcoming t h i s problem. A b r i e f e x a m i n a t i o n o f the method i n w h i c h mammals overcome t h e n o i s e problems may# t h e r e f o r e , throw some l i g h t on t h e p o s s i b l e mechanisms used by f i s h . / Bekesy's p r o p o s a l was t h a t t h e nervous system p o s s e s s e d an a b i l i t y t o f u n n e l p a r t i c u l a r b i t s o f i n f o r m a t i o n w h i l e r e j e c t i n g o r a t t e n u a t i n g o t h e r i n f o r m a t i o n . H i s arguments, when a p p l i e d t o t h e a u d i t o r y system produced a conc e p t o f t h e a c o u s t i c f i e l d as one where a p a r t i c u l a r sound, t h e one t h e o b s e r v e r wished to h e a r was c e n t r a l i s e d i n t he f i e l d , and the e f f e c t o f s u r r o u n d i n g a c o u s t i c s t i m u l i was a t t e n u a t e d . T h i s concept o f t h e a c o u s t i c f i e l d i s analagous w i t h t h e v i s u a l f i e l d p e r c e i v e d by t h e o p t i c system. - 108 -P f a l z (1962) drew s u p p o r t f o r Bekesy's f u n n e l i n g t h e o r y f r o m n e u r o p h y s i o l o g i c a l e x p e r i m e n t s he performed on mammalian a u d i t o r y s ystems. He found the d i s c h a r g e i n secondary neurones i n t h e c o c h l e a r n u c l e i t o be maximal at an optimum f r e q u e n c y , but t h e neurones were found not to respond t o o t h e r f r e q u e n c y r a n g e s . P f a l z r e a l i s e d t h a t h i s e v i d e n c e i n c o l l a b o r a t i o n w i t h e x p e r i m e n t a l e v i d e n c e o b t a i n e d by Fex (1962), from i n v e s t i g a t i o n s performed on t h e mammalian o l i v o - c o c h l e a r b u n d l e , i n d i c a t e d t h e e x i s t e n c e o f a mechanism f o r s h a r p e n i n g s e n s a t i o n . I n t h i s c a s e i t was l o u d n e s s . There i s e v i d e n c e t o i n d i c a t e t h a t a mechanism f o r n e u r a l f u n n e l i n g e x i s t s even i n t h e l o w e s t l e v e l s o f t h e a u d i t o r y system. I f a background n o i s e a t t e n u a t i n g mechanism o p e r a t i n g 0 a l o n g s i m i l a r l i n e s t o the o l i v o - c o c h l e a r bundle s e r v e s t h e l a t e r a l l i n e o rgans o f f i s h e s then i t i s e x p e c t e d t h a t such a mechanism would s h a r e some o f the fundamental c h a r a c t e r i s t i c s o f t h e o l i v o - c o c h l e a r b u n d l e . P e r i p h e r a l e v i d e n c e o f t h e e x i s t e n c e o f t h e o l i v o - c o c h l e a r bundle i s i n d i c a t e d by t h e e f f e r e n t i n h i b i t o r y i n n e r v a t i o n o f the c o c h l e a r h a i r c e l l s w h i c h i s s e n s i t i v e t o a c o u s t i c s t i m u l a t i o n o f b o t h t h e i p s i l a t e r a l and c o n t r a l a t e r a l e a r s . R e s u l t s o f n e u r o p h y s i o l o g i c a l i n v e s t i g a t i o n s o f t h e i n n e r v a t i o n of t h e a n t e r i o r l a t e r a l l i n e system i n the g o l d f i s h d emonstrated t h e e x i s t e n c e o f e f f e r e n t i n n e r v a t i o n t o s i n g l e o r g a n s . T h i s i n n e r v a t i o n , w h i l s t b e i n g i n h i b i t o r y , - 109 -c o u l d not be shown t o be a c o u s t i c a l l y s e n s i t i v e . The i n t e r -a c t i o n between a f f e r e n t and e f f e r e n t n e r v e s i n n e r v a t i n g a s i n g l e neuromast however, was not i n v e s t i g a t e d . I f t h e a c t i v i t i e s o f t h e a f f e r e n t and e f f e r e n t f i b e r s i n n e r v a t i n g a s i n g l e l a t e r a l l i n e organ can be shown t o be i n t e r d e p e n d e n t , and t h a t t h i s i n t e r d e p e n d e n c e can be shown t o be t h e most p e r i p h e r a l p a r t o f a n o i s e a t t e n u a t i n g system, t h e n i t must be assumed t h a t i f such an a t t e n u a t i n g system e x i s t e d t h e most p e r i p h e r a l p a r t of t h e mechanism i s o p e r a t i v e on t h e a c t i v i t i e s o f second o r d e r l a t e r a l l i n e neurones B ( F i g u r e 12a). T h i s c r i t e r i u m has been put f o r w a r d s i n c e i t i s assumed t h a t by v i r t u e of i t s n a t u r e , a n o i s e a t t e n u a t i n g system must be a c o u s t i c a l l y s e n s i t i v e . However, e f f e r e n t f i b e r s do not appear t o be a c o u s t i c a l l y s e n s i t i v e , and s i n c e t h e s e are p r o p o s e d , as a minimum, h y p o t h e s i s , t o be o p e r a t i v e a t f i r s t o r d e r neurones A ( F i g u r e 1 2 a ) , t h e a t t e n u a t i n g system i s p roposed to o p e r a t e a t h i g h e r s e n s o r y l e v e l s t h a n t h e s e neurones. On the o t h e r hand i t i s p o s s i b l e t h a t t h e a c t i v i t y o f t h e e f f e r e n t s i n f i s h e s are dependent of t h e a f f e r e n t a c t i v i t y , i n w h i c h case a n o i s e a t t e n u a t i n g system c o u l d be o p e r a t i v e a t f i r s t o r d e r neurones. The f i r s t p o s s i b i l i t y o f a n o i s e a t t e n u a t i n g system E ( F i g u r e 12a) a c t i n g at second o r d e r neurones has been shown. . An a t t e n u a t i n g system at t h i s l e v e l , i f i t f o l l o w e d t h e p a t t e r n o f a c t i o n o f the o l i v o - c o c h l e a r b u n d l e , would - 110 -c o n s i s t o f i n h i b i t o r y neurones E w h i c h would a t t e n u a t e a c t i v i t y r e s u l t i n g from n o i s e i n second o r d e r neurones B. The a c t i v i t y i n E would o f n e c e s s i t y be s e n s i t i v e t o a c o u s t i c s t i m u l a t i o n , and t h e r e c e p t i o n o f t h i s would be -through a f f e r e n t a c t i v i t y f r o m o t h e r neuromasts. However, the d e t e c t i o n of n o i s e by t h e l a t e r a l l i n e organs i s dependent upon t h e o r i e n t a t i o n o f t h e o r g a n . The d i s p l a c e -ments caused by n o i s e have components i n a l l p l a n e s , and t h e s e components w i l l have d i f f e r e n t v a l u e s from each o t h e r . Thus th e a c o u s t i c i n f o r m a t i o n t o E would have t o be con-t r i b u t e d by a p o p u l a t i o n o f l a t e r a l l i n e organs o r i e n t a t e d i n t h e same p l a n e as t h e l a t e r a l l i n e organs under c o n s i d e r a t i o n . A l t h o u g h the e f f e r e n t a n t e r i o r l a t e r a l l i n e n e r v e s were not demonstrated t o be a c o u s t i c a l l y s e n s i t i v e , t h e y were f o u n d t o be s e n s i t i v e t o g e n e r a l m u s c u l a r a c t i v i t y i n the body. The s i g n i f i c a n c e o f t h i s dependence i s not at p r e s e n t f u l l y r e a l i s e d , and i t was s u g g e s t e d e a r l i e r t h a t t h e dependence may be c o r r e l a t e d w i t h an i n c r e a s e d r e sponse r a t e o f the f i s h t o s t i m u l a t i o n by w a t e r d i s p l a c e m e n t s . However, a c o n s i d e r a t i o n o f t h e c e n t r a l c o n n e c t i o n s of the a n t e r i o r l a t e r a l l i n e n e r v e s has l e a d t o a s u g g e s t i o n f o r the r o l e o f t h e e f f e r e n t s . The a n t e r i o r l a t e r a l l i n e n e r v e e n t e r s t h e b r a i n and d i v i d e s i n t o d o r s a l and v e n t r a l r o o t s , and t h e v e n t r a l r o o t e s p e c i a l l y becomes c l o s e l y a s s o c i a t e d w i t h t h e v e s t i b u l a r n e r v e (Kappers, Hubers and Crosby 1955). W h i l e - I l l -F i g u r e 12 A A model c o n s t r u c t e d t o show t h e arrangement of t h e proposed n o i s e a t t e n u a t i n g system a c t i n g upon second o r d e r l a t e r a l l i n e neurones i n t h e m e d u l l a of a g o l d f i s h . A i s a f i r s t o r d e r l a t e r a l l i n e neurone. B i s a second o r d e r l a t e r a l l i n e neurone. C i s an i n h i b i t o r y e f f e r e n t neurone. D i s a motor c e n t r e neurone. E i s a n o i s e a t t e n u a t i n g i n h i b i t o r y neurone. B A model i l l u s t r a t i n g t h e p o s s i b l e r o l e o f t h e l a t e r a l l i n e system as a p a r t o f a mechanism f o r the r e f l e x c o n t r o l o f swimming. N i s a l a t e r a l l i n e organ M i s a Mauthner neurone i n n e r v a t i n g a motor neurone. T i s a t r u n k myotome on t h e c o n t r a l a t e r a l s i d e of t h e t a i l o f t h e f i s h . E i s an i n h i b i t o r y e f f e r e n t neurone i n n e r v a t e d by a p r o p r i o c e p t i v e neurone. C.N.S A - 112 -t h e s m a l l e r d o r s a l r o o t s t e r m i n a t e m a i n l y i n t h e c e r e b e l l u m and p o s t e r i o r l a t e r a l l i n e l o b e s o f b oth t h e i p s i l a t e r a l and c o n t r a l a t e r a l s i d e s of the b r a i n , many of t h e v e n t r a l r o o t f i b e r s t e r m i n a t e i n t h e a n t e r i o r l a t e r a l l i n e l o b e , and some t h i c k f i b e r s c l o s e l y accompany t h e v e s t i b u l a r n e r v e . These t e r m i n a t e t o g e t h e r i n t h e r e g i o n o f t h e n u c l e u s t a n g e n t i a l i s and t h e Mauthner Neurones. T h e i r t h i c k n e s s and d i r e c t c o n n e c t i o n w i t h t h e motor tegmentum of t h e m e d u l l a o b l o n g a t a l e a d Kapper, Hubers and Crosby t o suggest t h a t c e n t r a l l y t h e v e n t r a l l a t e r a l l i n e r o o t s were concerned w i t h t h e e s t a b l i s h m e n t o f r e f l e x pathways t o motor c e n t r e s . . S t e p h a n e l l i (1951) p r e s e n t e d e v i d e n c e w h i c h c o l l a b o r a t e d w i t h t h e a n a t o m i c a l e v i d e n c e of Kapper, Hubers and C r o s b y . He showed i n Xenopus, d u r i n g a s t u d y o f metamorphosis, t h a t t h e Mauthner a p p a r a t u s can o n l y e x i s t when b o t h t h e s e n s o r y systems o f t h e l a t e r a l l i n e and the motor s y s t e m of t h e t a i l were p r e s e n t . The absence o r s l i g h t development of o n l y one o f t h e s e systems was f o u n d t o be s u f f i c i e n t t o a l l o w i n v o l u t i o n o r none d i f f e r e n t i a t i o n o f t h e Mauthner Neurones. He c o n c l u d e d a l s o t h a t a d i f f e r e n c e i n t h e r a t e o f d i f f e r e n t i a t i o n shown by t h e Mauthner a p p a r a t u s i n t e l e o s t s , u r o d e l e s , and anurans was a f u r t h e r p r o o f t h a t i t s f u n c t i o n was r e l a t e d t o t h e a c t i v i t y o f swimming by movements of t h e t a i l and was d i r e c t l y c o n n e c t e d w i t h t h e l a t e r a l l i n e so as t o e s t a b l i s h a r e f l e x a c t i v i t y i n v o l v i n g t h e o r g a n . - 113 -. The d i s c o v e r y of t h e s e n s i t i v i t y o f t h e e f f e r e n t a n t e r i o r l a t e r a l l i n e f i b e r s t o mu s c u l a r a c t i v i t y and t h e c o l l a b o r a t i n g e v i d e n c e d e s c r i b e d above has l e a d t o t h e f o r m u l a t i o n o f a model ( F i g u r e 12b). The Mauthner neurones are two c o n s p i c u o u s neurones i n t h e m e d u l l a o b l o n g a t a w h i c h r e c e i v e t h e i r i n p u t p r i n c i p a l l y f r o m motor and v e s t i b u l a r c e n t r e s . They i n n e r v a t e the motor neurones c o n t r o l l i n g c o n t r a c t i o n o f c o n t r a l a t e r a l t r u n k myotomes by means o f a g i a n t axon w h i c h c o u r s e s down t h e c o n t r a l a t e r a l s i d e o f t h e s p i n a l c o r d . S t i m u l a t i o n o f t h e v e s t i b u l a r X I I I n e r v e on one s i d e o f t h e f i s h l e a d s t o an i n c r e a s e i n t h e e x c i t a b i l i t y o f t h e i p s i l a t e r a l Mauthner neurones, i n h i b i t i o n o f the c o n t r a l a t e r a l Mauthner neurone and c o n t r a c t i o n o f t h e c o n t r a l a t e r a l t r u n k myotomes ( R e t z l a f f 1954) (Furukawa and Fusshpan 1963). Because t h e a n t e r i o r , v e n t r a l , l a t e r a l l i n e r o o t f i b e r s a re i n c l o s e a s s o c i a t i o n w i t h t h e v e s t i b u l a r n e r v e s , t h e y have been assumed t o i n n e r v a t e t h e i p s i l a t e r a l Mauthner neurones i n the same manner. I n t h e model ( F i g u r e 12b) s t i m u l a t i o n o f t h e l a t e r a l l i n e organ N l e a d s t o an i n c r e a s e d a c t i v i t y i n t h e Mauthner C e l l , M, and an i n c r e a s e d r a t e o f c o n t r a c t i o n o f t h e t r u n k myotome muscles T. T h i s model, a l t h o u g h n o t shown, i s c o n s i d e r e d t o e x i s t on b o t h s i d e s o f t h e f i s h , so t h a t i n c r e a s e d a c t i v i t y i n t h e a n t e r i o r l a t e r a l l i n e o rgans would r e s u l t i n an i n c r e a s e d r a t e o f swimming. T h i s system by i t s e l f c o n s t i t u t e s a p o s i t i v e f eedback system, s i n c e .... - 114 -as t h e f i s h swims so t h e l a t e r a l l i n e becomes s t i m u l a t e d by w a t e r d i s p l a c e d down the s i d e s o f i t s body, and t h i s , i n t u r n r a i s e s t h e a c t i v i t y o f the Mauthner neurones. C o n s e q u e n t l y the t r u n k myotomes c o n t r a c t more s t r o n g l y and the f i s h swims f a s t e r . The i n h i b i t o r y e f f e r e n t f i b e r E i s shown i n t h e model ( F i g u r e 12b) t o be i n n e r v a t e d by p r o p r i o c e p t o r s i n t h e t r u n k myotomes. Only one i n t e r c a l a t e d neurone i s shown, but t h i s i s t o be t a k e n as t h e minimum h y p o t h e s i s s i n c e no doubt i f t h i s feedback system does e x i s t , i t would be more complex th a n t h i s . C o n t r a c t i o n o f t h e c o n t r a l a t e r a l t r u n k myotomes l e a d t o i n h i b i t i o n o f t h e i p s i l a t e r a l a n t e r i o r l a t e r a l l i n e o r g a n s . The s t r o n g e r t h e c o n t r a c t i o n of t h e m u s c l e s , th e g r e a t e r t h e i n h i b i t i o n . These two systems, t h e one t e n d i n g t o i n c r e a s e the a c t i v i t y o f t h e t r u n k myotomes, and the o t h e r s u p p r e s s i n g t h e a c t i v i t y o f t h e a n t e r i o r l a t e r a l l i n e o r g a n s , i f t h e y a c t e d t o g e t h e r , would l e a d to a r e g u l a t i o n o f swimming v e l o c i t y . There i s some b e h a v i o u r a l e v i d e n c e ( D i j k g r a a f 1963) t o s u p p o r t t h e i d e a t h a t l a t e r a l l i n e organs do p l a y a p a r t , under c e r t a i n c o n d i t i o n s , i n r e g u l a t i n g swimming v e l o c i t y . D i j k g r a a f o b s e r v e d t h a t minnows d e p r i v e d o f t h e i r l a t e r a l l i n e o rgans had d i f f i c u l t y i n m a i n t a i n i n g r e g u l a t e d swimming v e l o c i t y , but were q u i t e a b l e t o m a i n t a i n t h e i r p o s i t i o n s i n l a r g e a p p l i e d w a t e r c u r r e n t s where, he b e l i e v e d , t a c t i l e s e n s a t i o n and v i s i o n were r e s p o n s i b l e . He a l s o n o t i c e d t h a t minnows k e p t i n an aquarium would swim a g a i n s t - 115 -t h e s m a l l c u r r e n t produced by w a t e r s t r e a m i n g i n t o t h e tank t h r o u g h t h e i n l e t p i p e , however i f d e p r i v e d o f t h e i r l a t e r a l l i n e organs t h e minnows f a i l e d t o make t h i s r e s p o n s e . From t h i s e v i d e n c e he c o n c l u d e d t h a t f i s h use t h e i r l a t e r a l l i n e o rgans when o r i e n t a t i n g i n i r r e g u l a r c u r r e n t s , and t h a t t h e y a l s o c o n t r i b u t e i n some way t o t h e r e g u l a t i o n o f swimming v e l o c i t y . Thus, i t i s c o n c l u d e d t h a t e x p e r i m e n t a l e v i d e n c e o b t a i n e d f o r the r o l e o f t h e e f f e r e n t nervous s u p p l y t o t h e a n t e r i o r l a t e r a l l i n e organs s u g g e s t s a motor r e f l e x r o l e f o r t h e e f f e r e n t s r a t h e r t h a n as p a r t o f a n o i s e a t t e n u a t i n g mechanism. - 116 -SUMMARY 1. On t h e o r e t i c a l grounds the l a t e r a l l i n e organs were i m p l i c a t e d as t h e a c o u s t i c a l l y s e n s i t i v e system w h i c h might be used by f i s h i f t h e y were c a p a b l e o f d i r e c t i o n a l l y h e a r i n g low f r e q u e n c y sound. I t was con-s i d e r e d t h a t f i s h might p o s s i b l y l o c a t e sound s o u r c e s by d e t e c t i n g t h e near f i e l d d i s p l a c e m e n t s a s s o c i a t e d w i t h them. 2. B o t h b l i n d g o l d f i s h and b l i n d cave f i s h demonstrated an a b i l i t y t o use t h e i r l a t e r a l l i n e organs t o d e t e c t w a t e r d i s p l a c e m e n t s a s s o c i a t e d w i t h , and hence d e t e c t , low f r e q u e n c y sound s o u r c e s and s t a t i o n a r y r o d s . 3. B l i n d cave f i s h were a b l e t o l o c a t e a sound s o u r c e a g a i n s t a background n o i s e o f c o n s t a n t f r e q u e n c y and a m p l i t u d e . A p h y s i o l o g i c a l n o i s e s u p p r e s s i n g mechanism, s i m i l a r t o t h a t found i n t h e mammalian c o c h l e a r was s u g g e s t e d to be a s s o c i a t e d w i t h t h e l a t e r a l l i n e system. 4. An e f f e r e n t nervous s u p p l y was found t o i n n e r v a t e t h e a n t e r i o r l a t e r a l l i n e o rgans of the g o l d f i s h . By t h e a p p l i c a t i o n o f a c o n v u l s a n t d r u g , s t r y c h n i n e s u l p h a t e , t o t h e l a t e r a l l i n e o r g a n s , i t was p o s s i b l e t o demonstrate t h e i n h i b i t o r y n a t u r e o f t h e s e e f f e r e n t f i b e r s . 5. The d i s c h a r g e r a t e o f the e f f e r e n t f i b e r s was found t o be u n a f f e c t e d by s t i m u l a t i o n o f o t h e r l a t e r a l l i n e o r g a n s , t o u c h r e c e p t o r s o r e a r s , and t o be i n s e n s i t i v e t o r e s p i r a t o r y movements. I t was shown, however, t o respond t o g e n e r a l i n c r e a s e d body m u s c u l a r - 117 -a c t i v i t y by an i n c r e a s e i n d i s c h a r g e r a t e . The hydrodynamic f i e l d about th e heads o f swimming g o l d f i s h were i n v e s t i g a t e d . The f i s h were o b s e r v e d t o a l t e r n a t e between two f l o w shapes d u r i n g r e s p i r a t i o n . They formed b l u f f b o d i e s when th e y had t h e i r mouths c l o s e d and g e n e r a t e d a bow wave, and became s t r e a m l i n e d when t h e i r mouths were open. T h i s c h a n g i n g c o n f i g u r a t i o n l e a d t o t h e p r o p o s a l t h a t t h e a n t e r i o r l a t e r a l l i n e organs f u n c t i o n e d b o th as v e l o c i t y d e t e c t o r s and n e a r f i e l d d i s p l a c e m e n t d e t e c t o r s . I t was c o n c l u d e d , f i r s t l y , f r o m e v i d e n c e p r e s e n t e d h e r e , and r e c e n t c o l l a b o r a t i n g e v i d e n c e t h a t l a t e r a l l i n e o rgans are a s h o r t range h e a r i n g system. S e c o n d l y , i t was thought t h a t i f a n e u r o p h y s i o l o g i c a l l y a c t i v e n o i s e s u p p r e s s i n g mechanism was a s s o c i a t e d w i t h the l a t e r a l l i n e system, i t was c o n f i n e d c e n t r a l l y t o t h e f i r s t o r d e r l a t e r a l l i n e n eurones. F i n a l l y , i t was s u g g e s t e d t h a t f i b e r s might be p a r t o f a system c o n t r o l l i n g m u s c u l a r movement, and i n v o l v i n g Mauthner neurones. A model was p r oposed. -118 -REFERENCES A d r i a n E.D., McK. C a t t e l l and H. Hoagland (1931) Sensory d i s c h a r g e s , i n s i n g l e cutaneous nerve f i b e r s . J . P h y s i o l . (Lond.) 72, 377. A l b e r s , V.M. (1960) Underwater A c c o u s t i c s Handbook. The P e n n s y l v a n i a S t a t e U n i v e r s i t y P r e s s . Bekesy, G. von (1958) F u n n e l i n g A c t i o n i n t h e Nervous System. J . A c o u s t . Soc. Am. 30, 399. Bekesy, G. von (1960) E x p e r i m e n t s i n H e a r i n g . M c G r a w - H i l l , New York. B e r g e i j k , W.A. von (1964) D i r e c t i o n a l and None D i r e c t i o n a l H e a r i n g i n F i s h . I n "Marine B i o - A c o u s t i c s " , (W.N. T r a v o l g a E d . ) , 281, Pergamon P r e s s . C u r t i s , D.R. (1962) The d e p r e s s i o n o f s p i n a l i n h i b i t i o n by e l e c t r o p h o r e t i c a l l y a d m i n i s t e r e d s t r y c h n i n e . I n t . J . Neuropharmacol. 1, 239. D e l C a s t i l l o , J . and B. K a t z (1957) A s t u d y o f c u r a r e a c t i o n w i t h an e l e c t r i c a l micro-method P r o c . Roy. Soc. B. 146, 339. Desmedt, J.E. (1962) A u d i t o r y - e v o k e d p o t e n t i a l s f r om c o c h l e a r t o c o r t e x as i n f l u e n c e d by a c t i v a t i o n o f t h e e f f e r e n t o l i v o -c o c h l e a r b u n d l e . J . A c o u s t . Soc. Am. 34, 1478. D i j k g r a a f , S. (1956) E l e c t r o p h y s i o l o g i s c h e Untersuchungen an d e r S e i t e n l i n i e von.Xenopus l a e v i s . E x p e r i e n t i a 12, 276. D i j k g r a a f , S. (1963) The f u n c t i o n i n g and s i g n i f i c a n c e o f the l a t e r a l l i n e o r g a n s . B i o l . Rev. 38, 51. E c c l e s , J.E. (1964) The P h y s i o l o g y of Synapses. Academic P r e s s . E c c l e s , J.E., P. F a t t and K. K o t e t s u , (1954), C h o l i n e r g i c and ' I n h i b i t o r y synapses i n a pathway from motor axon c o l l a t e r a l s t o motor-neurones. J . P h y s i o l . (Lond.) 216, 524. .Enger, P.S. (1966) The n e a r - f i e l d e f f e c t on sound t h r e s h o l d s i n g o l d f i s h . - C o n f e r e n c e on L a t e r a l L i n e D e t e c t o r s , New York. U n p u b l i s h e d . F e l d b e r g , W. (1963) A P h a r m a c o l o g i c a l Approach to t h e B r a i n . Edward A r n o l d L t d . Fex, J . (1962) A u d i t o r y a c t i v i t y i n c e n t r i f u g a l and c e n t r i p e t a l c o c h l e a r f i b e r s i n c a t s . A c t a P h y s i o l . Scand. S u p p l . 55. - 119 -F l o c k , A. (1966) F u n c t i o n a l A s p e c t s on t h e U l t r a - s t r u c t u r e and I n n e r v a t i o n of L a t e r a l L i n e H a i r C e l l s . C o n f e r e n c e on L a t e r a l L i n e D e t e c t o r , New Yo r k . U n p u b l i s h e d . F l o c k , A. and J . W e r s a l l , (1962), S y n a p t i c s t r u c t u r e s i n t h e l a t e r a l l i n e c a n a l organ o f t h e t e l e o s t f i s h l o t a v u l g a r i s . J . C e l l , B i o l . 13, 337. F r i s c h , K. von and H. S t e t t e r (1932) Untersuchungen uber den s i t z d e r G e h o r s i n n e s b e i d e r E l r i t z e . Z. v e r g l . P h y s i o l . 17, 686. F r i s c h , K. von and S. D i j k g r a a f , (1935) Konnen F i s c h e d i e S c h a l l r i c h t u n g vahrnehmen? Z. v e r g l . P h y s i o l . 22, 641. Furukawa, T. and E . J . Fusshpan, (1963), Two i n h i b i t o r y mechanisms i n t h e Mauthner neurones of g o l d f i s h . J . N e u r o p h y s i o l . 26, 140. Galambos, R. (1956) S u p p r e s s i o n o f a u d i t o r y n e r v e a c t i v i t y by s t i m u l a t i o n o f e f f e r e n t f i b e r s t o t h e c o c h l e a r . J . N e u r o p h y s i o l . 19, 424. Gorner, P. (1966) Independent o f a f f e r e n t a c t i v i t y f r o m e f f e r e n t a c t i v i t y i n the l a t e r a l l i n e organ o f Xenopus l a e v i s . C o n f e r e n c e on L a t e r a l L i n e D e t e c t o r , New York. U n p u b l i s h e d . H a r r i s , G.F. (1964) C o n s i d e r a t i o n s on t h e p h y s i c s o f sound p r o d u c t i o n by f i s h e s . I n "Marine B i o - A c o u s t i c s " (W.N. T a v o l g a Ed.) 233, Pergamon P r e s s . H a r r i s , G.G. and W.A. von B e r g e i j k (1962) E v i d e n c e t h a t t h e l a t e r a l l i n e organs respond t o nea r f i e l d d i s p l a c e m e n t s o f sound s o u r c e s i n w a t e r . J . A c o u s t . Soc. Amer. 34, 1831. H e r r i c k , C .J., (1899), The c r a n i a l and f i r s t s p i n a l n e r v e s o f M e n i d i a ; a c o n t r i b u t i o n upon t h e ne r v e components o f t h e boney f i s h e s . J . Comp. N e u r o l . 9, 153. # K a p p e r s , C.V.A., G.C. Huber and E.C. Crosby (1965) The Com-p a r a t i v e anatomy o f the nervous system o f v e r t e b r a t e s i n c l u d i n g man. Volume 1. H a f n e r P u b l i s h i n g Co. New York. K a t s u k i , Y. and S. Yoshi n o (1952) Response o f the s i n g l e l a t e r a l l i n e n e r v e f i b e r t o t h e l i n e a r l y r i s i n g c u r r e n t s t i m u l a t i n g the end o r g a n . J a p . J . P h y s i o l . 2, 219. K a t s u k i , Y.,S. Yoshi n o and J . Chen, (1951), A c t i o n c u r r e n t o f the s i n g l e l a t e r a l l i n e n e r v e f i b e r o f f i s h I I . On t h e d i s c h a r g e due t o s t i m u l a t i o n . J a p . J . P h y s i o l . 1, 179. - 120 -K l e e r k o p e r , H. and E.C. Chagnon, (1954), H e a r i n g i n f i s h , w i t h s p e c i a l r e f e r e n c e t o s e m o t i l u s a t r o m a c u l a t u s a t r o m a c u l a t u s ( M i t c h i l l ) J . F i s h e r i e s Res. Bd. Canada, 11, 130. K u i p e r , J . (1966) V i b r a t i o n s e n s i t i v i t y o f the l a t e r a l l i n e o f f i s h e s . C o n f e r e n c e on L a t e r a l L i n e D e t e c t o r s , New York. U n p u b l i s h e d . McPherson, M.B. and R.C. Nece, (1950) An i n e x p e n s i v e d e m o n s t r a t i o n f l u i d p o l a r o s c o p e . I s s u e d at the S p r i n g meeting o f the M i d d l e A t l a n t i c S e c t i o n o f t h e American Soc. Eng. E d u c a t i o n . Murray, R.W. (1955) The l a t e r a l i s organs and t h e i r i n n e r v a t i o n i n Xenopus l a e v i s . Q u a r t. J . M i c r o Sec. 96, 351. P a r k e r , G.H. (1902) H e a r i n g and a l l i e d senses i n f i s h e s . B u l l . U.S. F i s h Comm. 22, 45. P f a l z , R. K . J . (1962) C e n t r i f u g a l i n h i b i t i o n o f a f f e r e n t s e c o n d a r y neurons i n t h e c o c h l e a r n u c l e u s by sound. J . A c o u s t . Soc. Am. 34, 1472. Pumphrey, R . J . (1950) H e a r i n g . Symp. Soc. exp. B i o l . 4, 3. R a n d a l l , D.J. and G. S h e l t o n (1963) The e f f e c t s o f changes i n e n v i r o n m e n t a l gas c o n c e n t r a t i o n s on the b r e a t h i n g and h e a r t r a t e of a t e l e o s t f i s h . Comp. Biochem. P h y s i o l . 9, 229. Rasmussen, G.L. (1946) An e f f e r e n t c o c h l e a r b u n d l e . Anat. R e c o r d . 82, 441. Rasmussen, G.L. (1960) E f f e r e n t f i b e r s o f t h e c o c h l e a r n e r v e and c o c h l e a r n u c l e u s . I n " N e u r a l Mechanisms o f t h e A u d i t o r y and V e s t i b u l a r Systems" (G.L. Rasmussen and W.L. W i n d l e , Eds.) Cha p t e r 8, 105. Thomas, S p r i n g f i e l d , I l l i n o i s . R e t z l a f f , E. (1954) N e u r o h i s t o l o g i c a l b a s i s f o r t h e f u n c t i o n i n g of p a i r e d h a l f - c e n t r e s . J . comp. N e u r o l . 101, 407. R h e i n h a r d t , F. (1935) Uber Richtungswahrnehmung b e i F i s c h e n besonders b e i d e r E l r i t z e ( P h o x i n u s l a e v i s ) und beim Zwergwels (Amiurus n e b u l o s u s ) . Z. v e r g l . P h y s i o l . 22, 570. Rosen, M.W. (1966) D i s c u s s i o n . C o n f e r e n c e on L a t e r a l L i n e D e t e c t o r s , New York. U n p u b l i s h e d . Sand', A. (1937) The mechanism o f t h e l a t e r a l sense organs o f f i s h e s . P r o c . Roy. Soc. B. 123, 472. Schmidt, R.S. (1965) Amphibian a c o u s t i c o - l a t e r a l i s e f f e r e n t s J . C e l l and Comp. P h y s i o l . 65, 155. - 121 -S t e p h a n e l l i , A. (1951) S t r u c t u r e and f u n c t i o n o f the Mauthner a p p a r a t u s . Quart. Rev. B i o l . 26, 17. Tanaka, Y. and S. K a t s u k i , ( 1 9 66). P h a r m a c o l o g i c a l i n v e s t i -g a t i o n s o f c o c h l e a r r e s p o n s e s and of o l i v o - c o c h l e a r i n h i b i t i o n . J . N e u r o p h y s i o l . 29, 95. T r o t t W.J. and E.N. L i d e , (1955) Two p r o j e c t o r n u l l method f o r c a l i b r a t i o n o f hydrophones at low audio and i n f r a s o n i c f r e q u e n c i e s . J . A c o u s t . Soc. Am. 27, 951. W a l t e r s , V. (1966) F u n c t i o n morphology o f t h e l a t e r a l l i n e system. C o n f e r e n c e on L a t e r a l L i n e D e t e c t o r s , New York. U n p u b l i s h e d . 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0104786/manifest

Comment

Related Items