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A histological study of the digestive tract and associated organs of the newt Triturus granulosus Skilton Simpson, Robert Edward 1941

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A HISTOLOGICAL STUDY OS1 THE DIGESTIVE TRACT AND ASSOCIATED ORGANS OF THE NEWT TRITURUS GRANULOSUS SKILTON by Robert Edward Simpson A Thesis submitted i n P a r t i a l F u l f i l m e n t of The Requirements f o r the Degree of MASTER OF ARTS i n the Department of ZOOLOGY The U n i v e r s i t y of B r i t i s h Columbia October, 1941 ACKNOWLEDGMENTS. I wish to express to Professor G. J . Spencer, under whose d i r e c t i o n t h i s work was c a r r i e d on, my s i n c e r e appre-c i a t i o n of h i s h e l p f u l suggestions and valuable c r i t i c i s m . To Professor W. A. Clemens, Head of the Department of Zoology and to Professor I . MoT. Cowan, my thanks f o r t h e i r k i n d l y i n t e r e s t at a l l times. I am g r e a t l y indebted to Pro f e s s o r A. H. Hutchinson, Head of the Department of Biology and Botany, f o r the use of photomiorographic apparatus and f o r h i s i n s t r u c t i o n of methods and technique i n Plant h i s t o l o g y . To my f e l l o w students, David Waddell and John Aldous, my s i n c e r e thanks f o r the valuable help they have given me i n the tak i n g of photomicrographs. - TAB L I Off OOMPMTS. 1 page I . I n t r o d u c t i o n • 2 I I . M a t e r i a l ..... 3 I I I . Taxonomy • 5 IV. Technique • 8 V. Gross Anatomy .. 13 VI. H i s t o l o g y 21 A. The mouth c a v i t y and pharynx ...... 21 B. The oesophagus. 31 G. The stomach 34 D. The small i n t e s t i n e .................. 37 E. The large i n t e s t i n e 41 F. The cloaca 43 G. The l i v e r 48 H. The pancreas 52 V I I . Summary 54 Bib l i o g r a p h y 56 E l a t e s 60 For the w r i t i n g of s c i e n t i f i c papers, the eminent mathematician W. S. Gosset gives the f o l l o w i n g advice: " F i r s t say what you are going to say, then say i t ; and f i n a l l y end by saying that you have s a i d i t . " Such repet t i o n as i s found i n t h i s t h e s i s w i l l consequently rest on that defence. I. INTRODUCTION* The work which f o l l o w s i s e n t i r e l y d e s c r i p t i v e and i s intended to present a more i n c l u s i v e study of the Urodele d i g e s t i v e system than has been found i n any of the l i t e r a t u r e at the w r i t e r ' s d i s p o s a l . The alimentary canal w i l l be examined p r o g r e s s i v e l y from the mouth to the cloaca and a d e s c r i p t i o n of the d i -g e s t i v e glands undertaken. The gross anatomy w i l l be con-sidered f i r s t , f o l l o w e d by the h i s t o l o g i c a l d e s c r i p t i o n s . The l i t e r a t u r e concerning amphibia g e n e r a l l y i s abun-dant but that concerning d e s c r i p t i v e h i s t o l o g y i s scarce. Most of the more recent, work on amphibia considers e i t h e r the morphogenesis of the animals or i s confined to such a narrow h i s t o l o g i c a l f i e l d that the data are sometimes d i f f i c u l t to c o r r e l a t e . / Noble's book "Biology of the Amphibia" i s a u t h o r i t a t i v e and e x c e l l e n t f o r general information but few h i s t o l o g i c a l references are given. In matters o f gross and f i n e anatomy, reference was made to the "Anatomy of the Salamander" by F r a n c i s , 1934. This i s an e x c e l l e n t piece of d e t a i l e d work and was found very u s e f u l f o r comparison w i t h T r i t u r u s granulosus. F i n a l l y reference to Benjamin F. Kingsbury's a r t i c l e "The H i s t o l o g i c a l S t r u c t u r e of the Enteron of Necturus maculatus" has proven an i n v a l u a b l e guide i n the h i s t o l o g i c a l study. I I . MATERIAL. Three d i f f e r e n t groups of newts were obtained f o r the purpose of s e c t i o n i n g and study. 1. T h i r t y Japanese newts ( T r i t u r u s pyrrogaster) were imported from a dealer i n b i o l o g i c a l supplies i n San Fran-c i s c o . This group was used f o r t r i a l work only. £. The second group of newts, l a t e r i d e n t i f i e d as T. granulosus, was obtained i n Stanley Park near Beaver Lake. In l a t e February and throughout March (the time depending l a r g e l y on the weather} the newts.come out o f h i b e r n a t i o n and migrate to the water to breed. The greater part o f the migration occurs at dusk, when they can be seen c r o s s i n g the path'to the lake and are comparatively easy to f i n d . During other seasons of the year, they are e i t h e r breeding i n the water or h i b e r n a t i n g i n damp ground,^ r o t t e n logs and swampy places . One n o t i c e a b l e p e c u l i a r i t y of t h i s group, kept f o r observation during the summer months, was, that although the bodies of the females became swollen w i t h eggs, none would l a y . In approximately three months' time, the eggs were absorbed and the females assumed t h e i r normal shape. 3. The t h i r d group, r e c e i v e d from B l i s s Landing, B. C. was found i n September at the bottom of an o l d w e l l . They seemed to be of the same species as those from Beaver'Lake but were of a more b r i l l i a n t colour, being d o r s a l l y a l i g h t e r brown and v e n t r a l l y a b r i g h t e r orange. 4 Groups (2) ana (5) were used i n preparing the h i s t o -l o g i c a l s l i d e s from which the study was made. I I I . TAXONOMY. (a) Glass, Order, Sub-order and Family ( F r a n c i s , T 3 4 ) . The newt i s placed i n the c l a s s Amphibia of the vertebr a t e s , because of i t s naked glandular s k i n devoid of sc a l e s ; i t s aquatic l a r v a e ; i t s three-chambered heart; two o c c i p i t a l condyles and the absence of any amnion or a l l a n t o i s around the developing embryo. The r e t e n t i o n of the t a i l by the adu l t s and the posses-sion of limbs of approximately equal s i z e , confine i t to the Order Urodela or Gaudata. The complete metamorphosis and the backward extension of the prevomerine te e t h to w e l l behind the i n t e r n a l nares l i m i t i t to the Sub-order Salamandroidae. The Sub-order c o n s i s t s of three F a m i l i e s , the Salaman-dridae, the Amphiumidae and the Plethodontidae. The newt belongs to the Family Salamandridae which i s cha r a c t e r i z e d mainly by the shape of the prevomerine t e e t h , by the opisthocoelus vertebrae, and by one or two other s k e l e t a l f e a t u r e s of minor importance. This f a m i l y i s d i v i d e d g e n e r a l l y i n t o "Salamanders and Newts". The former are completely t e r r e s t r i a l i n the adult stage, while the l a t t e r show s t r o n g l y marked aquatic tenden-c i e s throughout l i f e , and are d e f i n i t e l y of a more p r i m i t i v e type. The Family i s made up of some eight genera, namely: Salamandra, Ohioglossa, T r i t u r u s , T y l o t o t r i t o n , P a c h y t r i t o n , Pleurodeles, Europroctus, and Salamandrina. Tliese genera are a l l Eurasian except f o r the American newts T r i t u r u s . '(Noble, '31). (b) Genus. (Noble, »3l). The c l a s s i f i c a t i o n of genera i s based on the characters of the bones of the head. In T r i t u r u s , the bony pterygoid i s small and does not reach the m a x i l l a r y , and the l a t t e r i s short not reaching the squamosal. There are other,, minor features of i d e n t i f i c a t i o n . (c) Species. (Twitty, 5 3 5 ) , Three species of T r i t u r u s occur on the P a c i f i c coast of North America, namely: T r i t u r u s torosus, T r i t u r u s r i v u l a r i s , and T r i t u r u s granulosus. These three species d i f f e r i n s e v e r a l respects but are so s i m i l a r t h a t i n v e s t i g a t o r s i n the past have oft e n mistaken one f o r the other. T w i t t y ( f 35) d i s t i n g u i s h e s and i d e n t i f i e s these species. Some of the d i f f e r e n c e s by which he d i s t i n g u i s h e s granulosus ( c i t e d as T_2_ s i m i l a n s ) from the others are enumerated below. ( i ) The heads of the breeding males are much broader than those of.the other species. ( i i ) The rows of p a l a t i n e t e e t h are s t r a i g h t and V-shaped without e i t h e r curves or bends. ( i i i ) The female c l o a c a during the breeding season assumes a c o n i c a l shape. ( i v ) The females i n c a p t i v i t y l a y eggs s i n g l y . (v) General. The species T^ torosus and T_»_ r i v u l a r i s are e x c l u s i v e l y C a l i f o r n i a n . A l l the T r i t u r i found i n extreme Northern C a l i f o r n i a and Oregon agree w i t h T^ granu-losus i n d i s t i n g u i s h i n g c h a r a c t e r i s t i c s ; they have orange rather than red v e n t r a l colour; y e l l o w i s h eyes; the larvae are broad finned and dotted r a t h e r than s t r i p e d ; and the breeding season i s l a t e * A l l these features agree with those of the newts used i n t h i s study, except one, the animals d i d not l a y i n c a p t i v i t y . There i s no doubt however that these newts are T r i t u r u s granulosus S k i l t o n ( F i t c h , '58, and S k i l t o n , 1849). 8 17* TECHNIQUE. M a t e r i a l * Only normal amphibian t i s s u e was used. The newts were decapitated w i t h s c i s s o r s and dropped immediately i n t o Bouin's f l u i d . A f t e r the outside t i s s u e had hardened f o r 15 minutes, the body was cut i n s e v e r a l pieces and returned again to the f i x a t i v e . A f t e r 12 to 18 hours f i x a t i o n , the sections were washed i n three changes of 70 per cent a l c o h o l u n t i l the p i c r i c a c i d was p r a c t i c a l l y removed. The pieces were then dehydrated and c l e a r e d i n dioxan, and imbedded i n wax. Sections were made through the mouth, pharynx, oesophagus, stomach, small i n t e s t i n e , l a r g e i n t e s t i n e , and cloaca. Although some d i f f i c u l t y was experienced i n s e c t i o n -ing the bone, t h i s was not considered enough to r i s k s p o i l i n g the s t a i n i n g p r o p e r t i e s of the t i s s u e w i t h a c i d d e c a l c i f i e r s . Sections of excised organs. Gross s e c t i o n s of the whole animal could not be made thinner than 12 u. For t h i s reason, sections were made of excised organs. P o r t i o n s of the oesophagus, stomach, small i n t e s t i n e , l a r g e i n t e s t i n e , and c l o a c a were removed, f i x e d , dehydrated, and embedded i n wax i n the usual manner. The l i v e r and pancreas were also excised and embedded. Results were very s a t i s f a c t o r y and sections could be cut at 6 u without d i f f i c u l t y . The mouth and pharynx were of n e c e s s i t y sectioned i n s i t u . F i x a t i o n . The f i x a t i v e f l u i d s used were: 1. Zenker's - At f i r s t Zenker's f i x a t i v e was used but r e s u l t s were not e n t i r e l y s a t i s f a c t o r y because the t i s s u e thus t r e a t e d was f r a n g i b l e . 2. Bouin's - This s o l u t i o n proved more s a t i s f a c t o r y than Zenker's and was used i n almost a l l o f the general work. 3. Regaud's F l u i d - This f l u i d was used i n f i x i n g the pancreas to preserve a c i d soluble granules and i n an attempt to demonstrate mitochondria. 4. A l c o h o l - Absolute a l c o h o l was used f o r f i x a t i o n before staining' f o r mucus. 5. Formalin - 10 per cent f o r m a l i n was used f o r f i x a t i o n p r i o r to s t a i n i n g f o r f a t . These f i x a t i v e f l u i d s were employed as d e t a i l e d i n Mal l o r y ' s " P a t h o l o g i c a l Technique". S t a i n i n g . 1. The general s t a i n . H a r r i s ' Haematoxylin and Congo red were found s a t i s -f a c t o r y f o r a l l g e n e r a l purposes. The haematoxylin showed the n uclear s t r u c t u r e s c l e a r l y while the Congo red used as a counter s t a i n gave more d i f f e r e n t i a t i o n than Eosin. An important m o d i f i c a t i o n o f the general s t a i n was used. The m a t e r i a l was f i r s t over-stained i n haematoxylin and then destained i n 70 per cent a c i d a l c o h o l u n t i l the cytoplasm was c l e a r but the n u c l e i were s t i l l w e l l s t a i n e d . A f t e r 10 s t a i n i n g i n Congo red, the s l i d e s were dehydrated i n dioxan as t h i s preserved the b r i l l i a n c y of the s t a i n whereas the higher a l c o h o l s tended to remove i t . The s l i d e s were then t r a n s f e r r e d to x y l o l and mounted i n xylol-balsam. I f the n u c l e i are w e l l stained, the r e s u l t s show a d i s t i n c t c o n t rast, the dark blue n u c l e i standing out against a b r i l l i a n t l y red background. This method i s very u s e f u l f o r general work. I t i s e a s i l y c o n t r o l l e d and uniform r e s u l t s can always be obtained. 2. M a l l o r y ' s T r i p l e (connective t i s s u e ) S t a i n . A f t e r Guyer This s t a i n was ex c e l l e n t and showed the connective t i s s u e s t r u c t u r e s much more c l e a r l y than d i d the general s t a i n . The nuclear s t r u c t u r e s were not as c l e a r however, and f o r t h i s reason the s t a i n was.usually employed without the a c i d f u s c h i n nuclear s t a i n . The connective t i s s u e f i b e r s (collagenous f i b r i l s ) stand out more sharply when the nuclear s t a i n i s omitted. This method was a l s o u s e f u l f o r demon-s t r a t i n g goblet c e l l s , and i n d i f f e r e n t i a t i n g the mucigenous border o f the g a s t r i c e pithelium. The a n i l i n e blue has an a f f i n i t y f o r mucin," the mucigenous p o r t i o n s of the s e c r e t i n g c e l l s s t a i n i n g a .deep blue. 3. S i l v e r Impregnation f o r Collagen and Reticulum. Foot's M o d i f i c a t i o n of Bielschowsky 1s Method. A f t e r M a l l o r y . R e t i c u l a r f i b e r s are brought out more c l e a r l y by t h i s 11 method than by any other. I t also demonstrates "terminal bars" w e l l . ;The method depends on the r e d i i c t i o n of the e a s i l y reducible s o l u b l e s i l v e r s a l t (an ammonium ion complex AgfNH^) ), formed by d i s s o l v i n g , w i t h ammonia, the p r e c i p i t a t e caused by adding a s o l u t i o n of sodium hydroxide to a s o l u t i o n of s i l v e r n i t r a t e . 4. Thionin s t a i n . This basic a n i l i n e dye was u s e f u l i n d i f f e r e n t i a t i n g c l e a r l y the lymphocytes invading the e p i t h e l i u m of the a l i -mentary c a n a l . These appeared a darker shade of blue than the n u c l e i of the surrounding c e l l s . The s t a i n was employed a f t e r Bouin's f i x a t i v e and no counter s t a i n was used. 5. Heidenhain's Iron Haematoxylin. A f t e r M a i l o r y . Congo red was used as a counter s t a i n . Tissue s t a ined by t h i s method showed no more than the general s t a i n and, as the s t a i n was not as s a t i s f a c t o r y to work with, the method was discarded. However s t a i n i n g f o r mitochondria a f t e r Regaud's f l u i d was f a i r l y s u c c e s s f u l . The mitochondria did not s t a i n s t r o n g l y but could be located by c a r e f u l examin-a t i o n . 6. Mayer's Mucicarmine S t a i n . A f t e r M a l l o r y . Mucin derived from e p i t h e l i a l c e l l s s t a i n s a b r i g h t red by t h i s method. The f i x a t i o n must be i n absolute a l c o h o l . 7. Sudan IV. S t a i n f o r Fat. A f t e r M a l l o r y . Demonstration of f a t i s s u c c e s s f u l i n unfixed t i s s u e s or a f t e r f i x i n g i n 10 per cent f o r m a l i n and c u t t i n g frozen 12 se c t i o n s . Fat ( s t a i n i n g b r i g h t red) was e a s i l y located i n the c e l l s of;the l i v e r and duodenum. Cl e a r i n g agents w i l l d i s s o l v e f a t s out of any r o u t i n e preparation. 8. Goodpasture's Eosin-Methyline Blue S t a i n f o r the Pancreas. A f t e r M a l l o r y . ' . This was, found a very s a t i s f a c t o r y s t a i n f o r the pancreas a f t e r f i x a t i o n w i t h Regaud's f l u i d . The zymogen granules show c l e a r l y and s t a i n a l i g h t purple colour. 13 Y. GROSS .ANATOMY. The various parts o f the d i g e s t i v e traot of I . granu-losus may be considered, f o r the purposes of d e s c r i p t i o n , i n the f o l l o w i n g order: mouth, pharynx, oesophagus, stomach, small i n t e s t i n e , l a r g e i n t e s t i n e , and cloaca; and the glands, l i v e r and pancreas. The alimentary canal o f T^ granulosus measures approxi-mately 20 cm. i n specimens averaging 20 cm. i n t o t a l length. The mouth. ( P l a t e I I I ) . The mouth i s the expanded a n t e r i o r p o r t i o n o f the d i g e s t i v e t r a c t and i s bounded above and below by the corres-ponding l i p s , which by t h e i r j u n c t i o n at the sides form the angles of the mouth. The l i p s are poorly defined and the cheeks are e n t i r e l y absent, hence there i s no v e s t i b u l e of the mouth as i n mammals. The c a v i t y of the mouth, the o r a l c a v i t y proper, i s the space s i t u a t e d between the dental arches. From each dental arch a r i s e s a row of homodont teeth The roof i s formed by the hard p a l a t e . On the palate two rows of prevomerine teeth a r i s e . Here a l s o are found the i n t e r n a l nares and a small median depression j u s t a n t e r i o r to the prevomerine teeth which r e c e i v e s the ducts of the i n t e r - n a s a l gland. The mucous membrane of the roof i s smooth The f l o o r i s formed, i n pa r t , by the rough d o r s a l surface of the tongue. L a t e r a l and a n t e r i o r to the tongue i s the p e r i u n g u a l r e g i o n which forms the remainder of the f l o o r . This surface i s covered by smooth e p i t h e l i u m which i s c a r r i e d 14 aoross from the deep surface of the gum to the v e n t r a l aspect of the tongue. The o r a l c a v i t y i s about 1.2 cm. i n width, measured tr a n s v e r s e l y at the angles of the mouth, and 1.7 cm. i n length, measured from the most a n t e r i o r part of the dental arch to the pharynx. The tongue i s small and c o n s i s t s merely of an o v a l pad which i s f i r m l y f i x e d to the f l o o r o f the mouth, but i s f r e e l a t e r a l l y and p o s t e r i o r l y . Walters f'40) st a t e s that i n higher amphibians, the adult tongue c o n s i s t s o f a g l a n d u l a r mass, the secondary tongue, superimposed upon a l a r v a l s t r u c -ture, the primary tongue. This i s the c o n d i t i o n i n T^ granu-losus. In the adult the secondary tongue i s the f u n c t i o n i n g s t r u c t u r e and i t s h i g h l y g l a n d u l a r e p i t h e l i u m i s thrown i n t o f o l d s so that the surface of the mucous l a y e r i s g r e a t l y increased. The primary tongue, Just v i s i b l e under the p o s t e r i o r edge of the secondary, i s small and non-glandular. The teeth are s m a l l , c o n i c a l s t r u c t u r e s b a r e l y v i s i b l e to the naked eye. They are arranged i n an arc on both the upper and lower jaws, as w e l l as i n two s t r a i g h t converging rows on the palate." These p a l a t i n e t e e t h are arranged along two dentigerous ridges on the prevomers. The patt e r n of the prevomerine teeth i s of taxonomic importance, (page 6) As a whole the t e e t h may be described as acrodont, homodont, and polyphyodont. 15 The pharynx. The pharynx leads d i r e c t l y from the mouth as a wide tube which passes imperceptibly into the oesophagus w i t h which i t i s continuous d o r s a l l y . V e n t r a l l y there i s a small s l i t - l i k e opening, the g l o t t i s , leading t o the larynx. There i s no naso-pharynx and there are no auditory tubes. The mucous membrane shows rudimentary l o n g i t u d i n a l f o l d s which become more prominent i n the oesophagus. The muscular w a l l s of the pharynx a r i s e f o r the most part from the base of the s k u l l ; hence the pharynx i s f i r m l y f i x e d i n t h i s p o s i t i o n . The oesophagus. ( P l a t e IV). The oesophagus extends from the pharynx to the stomach as a tube some 2 to 2.5 cm. i n length. E x t e r n a l l y there i s no c l e a r l i n e of demarkation between the oesophagus and the stomach, but i n t e r n a l l y the d i s t i n c t i o n i s c l e a r l y defined by the p a t t e r n o f f o l d s i n the mucous membrane. In the oesophagus the f o l d s are deep and l o n g i t u d i n a l i n d i r e c t i o n , while i n the stomach the f o l d s are shallow and form a wide meshed i r r e g u l a r pattern o f which the l o n g i t u d i n a l members are the most prominent. ( P l a t e I V ) . The stomach. ( P l a t e V). The stomach i s a conspicuous enlargement between the oesophagus and the i n t e s t i n e . It shows great d i s t e n s i b i l i t y and v a r i e s i n shape according to the amount of food contained. When empty i t i s sp i n d l e shaped, 2 cm. long, and l i e s almost l o n g i t u d i n a l l y along the l e f t side of the body. At i t s p o s t e r i o r end i t narrows considerably, turns sharply to the r i g h t and ends i n a w e l l marked c o n s t r i c t i o n , the p y l o r i c s p h i n c t e r . This c o n s t r i c t i o n i s more apparent when the stomach i s distended. In the a n t e r i o r or fundic p o r t i o n of the stomach, the epithelium (already described, page 15) i s r e l a t i v e l y f l a t , but i n the p y l o r i c region w e l l developed l o n g i t u d i n a l f o l d s are manifest. The small i n t e s t i n e * ( P l a t e V I ) . The small i n t e s t i n e i s subdivided i n t o : (a) the duodenum and (b) the small i n t e s t i n e proper. (a) The duodenum f o l l o w s a tranverse d i r e c t i o n r e l a t i v e to the body and i s i n d i s t i n g u i s h a b l e from the r e s t o f the i n t e s t i n e except that i t r e c e i v e s the pancreatic and b i l e ducts. This part of the i n t e s t i n e i s 1 .cm. i n length and £ to 3 mm. i n diameter. I t begins at the p y l o r i c sphincter and ends just p o s t e r i o r to the entrance of the common b i l e duct. (b) The small i n t e s t i n e proper i s a c o i l e d tube o f regular diameter approximately equal to or s l i g h t l y smaller than that of the duodenum. I t s l e n g t h i s about one-half that of the whole canal, i . e . , 10 cm. The e n t a l surface of the small i n t e s t i n e i s marked by l o n g i t u d i n a l f o l d s of the mucosa. These f o l d s are l a r g e r and more sinuous p r o x i m a l l y , i . e . , i n the duodenum, while d i s t a l l y they tend to become smaller and s t r a i g h t e r . The d i s t a l part of the small i n t e s t i n e opens i n t o the l a r g e i n t e s t i n e through an o r i f i c e guarded by a poo r l y developed 17 sphincter. The l a r g e ' i n t e s t i n e . The large i n t e s t i n e i s d i v i d e d i n t o : (a) a l a r g e , a n t e r i o r , s a c - l i k e p o r t i o n , the colon. ( P l a t e V I ) . (b) a short narrow p o s t e r i o r p o r t i o n , the rectum. ( P l a t e V I I ) . (a) The colon a r i s e s abruptly from the p o s t e r i o r end of the small i n t e s t i n e and measures approximately 2 cm. i n length. When i t i s expanded i t s w a l l s are very t h i n and i t s e p i t h e l i a l l i n i n g i s f l a t , but when i t i s empty the mucosa i s thrown i n t o sharp f o l d s . (b) The mucosa of the rectum i s thrown up i n t o permanent l o n g i t u d i n a l f o l d s which may almost f i l l the lumen of the empty tube. The w a l l s , p a r t i c u l a r l y the c i r c u l a r muscle l a y e r , become t h i c k e r and form a sphincter or valve-l i k e area. I t i s probable that the s p h i n c t e r of t h i s region c o n t r o l s the passage of the foeces to the outside, the cloaca being merely a t r a n s m i t t i n g chamber. The opening of the rectum into the cloaca i s properly c a l l e d the anus. The clo a c a . The cloaca i s the chamber p o s t e r i o r to the t e r m i n a l sphincter o f the rectum and extending to the e x t e r n a l aper-t u r e . Because t h i s chamber d i f f e r s g r e a t l y i n the male and female, the sexes w i l l be considered separately. 18 The male cloaca. ( P l a t e s V I I , I X ) . The c a v i t y of the male cloaca i s not a simple one. I t i s divided i n t o : (a) A dorsal tubular p o r t i o n , the c l o a c a l tube (Kingsbury, '96). A n t e r i o r l y t h i s c l o a c a l tube i s d i r e c t l y continuous with the rectum. L o n g i t u d i n a l f o l d s s i m i l a r to but smaller than those of the rectum mark the w a l l s . The W o l f f i a n ducts enter t h i s tube d o r s a l l y on the t i p s of two small u r o g e n i t a l p a p i l l a e , s i t u a t e d on e i t h e r side of the mid l i n e , while the bladder opens as a l o n g i t u d i n a l s l i t i n the v e n t r a l w a l l immediately below the u r o g e n i t a l p a p i l l a e . The tube i t s e l f enters p o s t e r o - v e n t r a l l y i n t o the c l o a c a l chamber. (b) A v e n t r a l c a v i t y , the c l o a c a l chamber (Kingsbury, '96). This chamber opens to the outside through the c l o a c a l aperture. From the chamber a d i v e r t i c u l u m extends a n t e r i o r l y , ventrad of the c l o a c a l tube. The c a v i t y of the d i v e r t i c u l u m i s d i v i d e d m e d i a l l y by a prominent p r o j e c t i o n from the antero-d o r s a l w a l l , the c l o a c a l p a p i l l a . The p a p i l l a i s lar g e and almost e n t i r e l y f i l l s the c a v i t y o f the d i v e r t i c u l u m but i t does not extend into the c l o a c a l chamber. The w a l l s of the d i v e r t i c u l u m and p a r t i c u l a r l y the w a l l s of the c l o a c a l chamber are thrown i n t o a s e r i e s o f l o n g i t u d i n a l f l a t topped r i d g e s . The l i p s surrounding the c l o a c a l aperture are also marked by w e l l defined f o l d s , which extend r a d i a l l y from i t s margin. Surrounding the cloaca i s a l a r g e g l a n d u l a r mass. This 19 mass i s divided i n t o three portions which correspond to the glands l o c a t e d i n the cloaca of T r i t o n by Heidenhain 1890 (Kingsbury, f96), namely: the c l o a c a l gland, the abdominal gland and the p e l v i c gland. The c l o a c a l gland i s the l a r g e s t and l i e s v e n t r a l l y e n t i r e l y surrounding the c l o a c a l chamber and d i v e r t i c u l u m except on t h e i r d o r s a l s i d e . The greater part of the mass of the w e l l developed abdominal gland l i e s post ero-dor s a l l y above the c l o a c a l tube, while the small p e l v i c gland also l i e s d o r s a l l y but more a n t e r i o r l y , i n a p o s i t i o n j u s t p o s t e r i o r to the entrance of the u r o g e n i t a l ducts i n t o the tube. Some of the tubules of the abdominal gland pass l a t e r a l l y and a n t e r i o r l y to the body of the p e l v i c gland, to form a small mass between the peritoneum and the body muscles i n the caudal end of the abdomen. The female c l o a c a . ( P l a t e s V I I I , I X ) . The cloaca of the female i s a simple chamber, i n t o which open the rectum, the ovi d u c t s , the u r e t e r s and the u r i n a r y bladder. S l i g h t l y p o s t e r i o r to the entrance of the rectum the oviducts enter on the t i p s of two large d o r s a l p a p i l l a e . The u r e t e r s also enter on the dor s a l w a l l s l i g h t l y caudad of the oviducts. No u r i n a r y p a p i l l a e occur. The opening of the bladder l i e s below the ovi d u c a l p a p i l l a e and antero-v e n t r a l to the anus. The e x t e r n a l aperture i s small but becomes c o n i c a l i n the breeding season. Prominent d o r s a l and l a t e r a l f o l d s occur on the w a l l s , and on the d o r s a l surface caudad of the u r e t e r s , a p a i r of pigmented patches 20 are found which mark the p o s i t i o n o f the spermathecae. The spermathecae -are microscopic i n s i z e and w i l l be considered with the h i s t o l o g y . The d i g e s t i v e glands. (a) The l i v e r i s a la r g e elongated body, only s l i g h t l y lobed. I t l i e s v e n t r a l l y and to the r i g h t of the stomach, completely suspended by mesenteries. In the f r e s h c o n d i t i o n i t i s dark red i n colo u r . (b) The pancreas i s i r r e g u l a r l y t r i a n g u l a r i n shape, l y i n g almost do r s a l t o the duodenum* between i t and the stomach. The adult pancreas, which appears to be a s i n g l e mass, i s a c t u a l l y a composite gland representing three out-growths of the embryonic gut, i . e . : two v e n t r a l and one d o r s a l ; ( F r a n c i s "34), but the three ducts are p e r s i s t e n t , the two v e n t r a l ones discharging i n t o the common b i l e duct, while the duct of the d o r s a l outgrowth opens d i r e c t l y i n t o the duodenum (determined by s e r i a l s e c t i o n s ) . In the f r e s h state the pancreas i s white i n col o u r tinged f a i n t l y red w i t h blood. This f a c t r e a d i l y d i f f e r e n t i a t e s the pancreas from the l i v e r . 21 VI. HISTOLOGY. A. The mouth c a v i t y and pharynx. The mouth c a v i t y and pharynx having many c h a r a c t e r i s -t i c s i n common w i l l be considered together. ( P l a t e s X to XV). The l i p s are represented by a f o l d i n the skin along the outer r i d g e o f the jaws, and at the crest of t h i s f o l d there i s a l o s s of the a l v e o l a r glands of the epidermis. The s t r a t i f i e d squamous epithelium of the epidermis continues past the ridges of the jaws i n t o the o r a l c a v i t y . Here a gradual t r a n s i t i o n and in t e r g r a d i n g of c e l l s takes place, from squamous epithe l i u m through cuboidal, to the s t r a t i f i e d low columnar e p i t h e l i u m which forms the l i n i n g of the g r e a t e r part o f the mouth c a v i t y and pharynx to the beginning o f the oesophagus. This e p i t h e l i u m contains numerous goblet c e l l s . The one exception to t h i s , gradual t r a n s i t i o n occurs on the p a l a t e j u s t w i t h i n the dental arch. Here a small area i s l o c a t e d i n which the epithe l i u m (8 to 10 c e l l s deep) i s t h i c k e r than elsewhere. T h i s r e g i o n i s composed of compact l a y e r s o f cuboidal c e l l s and few goblet c e l l s . The e p i t h e l i u m l i n i n g the o r a l c a v i t y and pharynx is', i n general, 3 to 5 c e l l s i n th i c k n e s s . The s u p e r f i c i a l c e l l s are short columns that are often l a t e r a l l y compressed by numerous swollen goblet c e l l s . Their n u c l e i are la r g e i n s i z e , oval i n shape and s t a i n l i g h t l y , although many dark chromatin granules may be seen i n them. The cytoplasm i s s l i g h t l y b a s o p h i l i c and non-granular. These surface c e l l s 22 show the so c a l l e d " c u t i o u l a r border" mentioned by Kingsbury (*94) as being found on the epithelium of the mouths of some amphibia, notably Neoturus, Proteus and Siredon. I t i s e a s i l y d i f f e r e n t i a t e d by the use o f a c i d stains,such as Congo red and A n i l i n e blue. The c e l l s of the basal l a y e r are considerably smaller than the s u p e r f i c i a l c e l l s , o v a l i n shape and r e g u l a r l y arranged on a d e f i n i t e basement membrane. They have a c e n t r a l , o v a l , densely b a s o p h i l i c nucleus and a l i g h t almost non-staining cytoplasm. The c e l l s of the intermediate region are i r r e g u l a r l y polygonal i n shape, and vary i n s i z e and s t a i n i n g p r o p e r t i e s between the c e l l s of the inner and outer l a y e r s . ( P l a t e X ) . Goblet c e l l s ( P l a t e X) are found i n a l l p a r t s of the ep i t h e l i u m but are most numerous on and j u s t p o s t e r i o r to the tongue. They are present i n every l a y e r of the e p i t h e l -ium, small ones reaching .down only one or two c e l l s from the surface and l a r g e r ones extending r i g h t down to the basement membrane. The morphology o f goblet c e l l s v a r i e s g r e a t l y i n the d i f f e r e n t f u n c t i o n a l phases. 1 The i n a c t i v e or r e s t i n g c e l l s bear a close resemblance to the p r i n c i p a l c e l l s of the e p i -thelium. Their d i s t a l ends g r a d u a l l y f i l l w i t h granules of mucigen and the c e l l s become swollen w i t h s e c r e t i o n . F i n a l l y the a c t i v e c e l l s assume the t y p i c a l goblet shape from which the name i s derived. The s e c r e t i o n distends the e n t i r e 23 d i s t a l p o r t i o n o f the c e l l s , and the n u c l e i , embedded i n a minute mass o f unaltered cytoplasm, are forced to the narrow base. In c e l l s extremely distended with s e c r e t i o n the n u c l e i are often f l a t t e n e d . This mucous s e c r e t i o n i s eventually extruded from the c e l l s , ( P l a t e XVII) and the w a l l s c o l l a p s e . Then the goblet c e l l s again become s i m i l a r to the p r i n c i p a l c e l l s . The granules of mucigen i n the goblet c e l l s are u s u a l l y destroyed i n f i x i n g w i t h Bouin's and Zenker's so that the c e l l body appears c l e a r and contains an a r t i f i c i a l network of cytoplasm and p r e c i p i t a t e d mucigen. This network s t a i n s i n a manner which i s t y p i c a l o f mucigen, i . e . , deeply w i t h Mucioarmine or A n i l i n e blue. When Regaud's f i x a t i v e i s employed the granules become apparent. Most of the e p i t h e l i a l surface i s n o n - c i l i a t e d but small scattered patches of c i l i a are found, p a r t i c u l a r l y on the roof of the mouth and pharynx. The c i l i a are short f i n e s t r u c t u r e s , and are apparently o f the non-motile "brush border" type. At the p o s t e r i o r extremity of the pharynx, c i l i a t e d c e l l s are found i n g r e a t e r numbers, possessing long c i l i a s i m i l a r to those found i n the oesophagus. Kingsbury ('94) s t a t e s that the o r a l e p i t h e l i u m of most amphibia i s c i l i a t e d , but that he found no c i l i a i n the mouths of Neoturus, Proteus, Siredon and Cryptobranchus. I t would seem that the o r a l e p i t h e l i u m of T^ granulosus i s i n an i n t e r -mediate c o n d i t i o n . 24 Kingsbury states f u r t h e r that sense organs, muoh resembling "the sense organs i n the mouths of f i s h e s , are found i n the o r a l e p i t h e l i u m of Necturus, Proteus, Siredon and Cryptobranchus but that no such organs are found i n Anura and Salamandridae. None were found i n the mouth of T. granulosus.• Below and supporting the epith e l i u m of the mouth c a v i t y , i s the lamina p r o p r i a , a densely organized l a y e r of extremely v a s c u l a r r e t i c u l a r t i s s u e . Beneath the lamina p r o p r i a i s a wider l a y e r of loose a r e o l a r t i s s u e forming the submucosa. This l a y e r i s a l s o r i c h i n blood v e s s e l s which i n t u r n supply the vessels o f the lamina p r o p r i a . I t serves to u n i t e the mucosa to the surrounding s t r u c t u r e s , i . e . , the bones of the roof of the mouth d o r s a l l y and the muscles of the throat and the hyo-b r a n c h i a l c a r t i l a g e s v e n t r a l l y . The tongue. ( P l a t e XIV). The v e n t r a l and l a t e r a l surface of the tongue i s covered w i t h an e p i t h e l i u m s i m i l a r to that which covers the rest of the o r a l c a v i t y . Over the f r e e edge of the tongue and upon i t s d o r s a l surface the f o l l o w i n g changes take place: ( l ) there i s an increase i n the s i z e and numbers of goblet c e l l s and (2) the e p i t h e l i u m i s thrown i n t o numerous i r r e g u l a r f o l d s . At the bases of these f o l d s open the tubules of the l i n g u a l glands. The l i n g u a l glands. ( P l a t e s XI, X I I ) . A gradual t r a n s i t i o n takes place "from the s u p e r f i c i a l 25 epithelium of the tongue to the simple pyramidal epithelium l i n i n g the "tubules of the l i n g u a l glands. These glands are tubular s t r u c t u r e s with one or more branches which i n some cases are very long and extend below the c a r t i l a g i n o u s hyo-b r a n c h i a l apparatus of the tongue. ( P l a t e I I I ) . At the peak of mucous secretion the c e l l s nearly f i l l the lumen of the glands, but f o l l o w i n g l i b e r a t i o n o f the secreted m a t e r i a l the c e l l s become shorter and the lumen becomes wider. The n u c l e i are l a r g e and s p h e r i c a l . They are s i t u a t e d at the bases of the c e l l s and u s u a l l y contain one or more conspicuous n u c l e o l i . The cytoplasm i s f i n e l y g r a n u l a r and s l i g h t l y b a s o p h i l i c . In the m a t e r i a l sectioned most of the glandular c e l l s are i n the a c t i v e l y s e c r e t i n g s t a t e . During t h i s period the cytoplasm i n the d i s t a l part of the c e l l i s c l e a r and a d e f i n i t e mucigenous network i s shown. At the base of the s e c r e t i n g c e l l s , between them and t h e i r basement membrane, occasional s m a l l crescent-shaped c e l l s , the demilunes of Heidenhain, occur. The voluntary muscle .situated i n the tongue corresponds i n p o s i t i o n to the M. genio-glos sus described by Francis ('34) i n Salamandra salamandra. I t consists,, o f two p o r t i o n s : (1) a mesial p o r t i o n composed of p a r a l l e l f i b e r s on e i t h e r side of the m i d - l i n e j u s t above the hyobranchial c a r t i l a g e s and (2) a second p o r t i o n i n which the f i b e r s are l o c a t e d i n the v e n t r o - l a t e r a l w a l l s . ( P l a t e I I I ) . 26 The i n t e r n a s a l gland. ( P l a t e X I I I ) . S i t u a t e d between the two n a s a l capsules l i e s the glan-dula i n t e r n a s a l i s or i n t e r m a x i l l a r i s , which discharges by two or three ducts i n t o the small median depression immediate-l y beneath the gland (page 13). This gland has been des-c r i b e d i n d e t a i l f o r European Urodeles by S e i f e r t ( F r a n c i s , '34). I t i s a compound tubular gland l i n e d w i t h columnar epithelium. The c e l l s l i n i n g the tubules, when i n the i n a c t i v e s t a t e , are almost without exception uniform i n s i z e and general s t r u c t u r e . Each c e l l i s t a l l and narrow w i t h a large s p h e r i c a l nucleus occupying the whole of i t s b a s a l p o r t i o n . The f i n e l y granular cytoplasm i s extremely baso-p h i l i c . These c e l l s when i n the a c t i v e s t a t e appear extremely swollen and possess a c l e a r cytoplasm s i m i l a r to that of the goblet c e l l s . Demilunes o f Heidenhain occur f r e q u e n t l y between the c e l l s o f t h i s gland. The ducts are l i n e d w i t h e p i t h e l i u m s i m i l a r to but lower than that described i n the tubules of the gland. No a c t i v e l y s e c r e t i n g c e l l s were observed i n them. S e i f e r t ( F r a n c i s , "34) found another group of glands i n Salamandra salamandra, the g l a n d u l a p a l a t i n a , which open i n t o small ducts at the bases o f the prevomerine t e e t h . No such glands could be located i n Tj_ granulosus. Kingsbury ( F r a n c i s , "34) a s s e r t s that he found aggre-gations of c e l l s of a lymphoid character i n as many as twelve regions of the mouth and pharynx of Salamandra, Necturus, Proteus 27 and others. He regarded these aggregations as analogous to the t o n s i l s " of Amniota. Most o f these areas are not constant i n p o s i t i o n but Kingsbury noted four of them that are, namely: (1) The choanal, i n the roof of the mouth immediately p o s t e r i o r to the i n t e r n a l n a r i a l opening. (2) The s u b l i n g u a l , l y i n g l a t e r a l to the tongue over the expanded cerato-hyal. (3) The l a t e r a l , s i t u a t e d l a t e r a l l y i n the pharynx i n the general region of the a r t i c u l a t i o n of the jaw. (4) The p r o g l o t t i d e a l , on the f l o o r of the mouth j u s t i n f r o n t of the g l o t t i s . Of these f o u r only two were d e f i n i t e l y located i n T. granulosus, the s u b l i n g u a l and the l a t e r a l . In these the epithelium appears thickened by the presence of many lymphocytes i n the deeper l a y e r s . This t h i c k e n i n g may even take the form of small f o l d s as i n the su b l i n g u a l area. ( E l a t e XIV). There i s no basement membrane and the lamina p r o p r i a invades the base o f the area, and supports i t w i t h a framework of r e t i c u l a r f i b e r s . No capsule or lymph sinuses are present and there i s no development i n t o a lymph gland or lymph nodule but the t i s s u e i s f u l l of lymphocytes and i s obviously lymphatic. Most of these lympho-cytes are small c e l l s , c o n t a i n i n g densely b a s o p h i l i c n u c l e i and l i t t l e cytoplasm. Large lymphocytes o c c a s i o n a l l y occur; t h e i r n u c l e i are l a r g e , roughly s p h e r i c a l , l e s s densely 28 s t a i n i n g than those of the smaller c e l l s , and are provided with w e l l developed n u c l e o l i * Below these lymphocytic areas, i n the lamina p r o p r i a , occur numerous c a p i l l a r i e s of l a r g e diameter, f i l l e d w i t h red blood c e l l s . ( P l a t e XIV). These enlarged c a p i l l a r i e s occur to a l e s s e r extent i n the mucosa of the o r a l c a v i t y and pharynx, where they are located just beneath the e p i -t h e l i a l l a y e r and correspond i n p o s i t i o n to the stratum vasculare of the amphibian s k i n . Their d i s t r i b u t i o n i s general but they are most numerous i n the pharynx. They are often so c l o s e l y associated w i t h the e p i t h e l i u m that they a c t u a l l y bulge up between the e p i t h e l i a l c e l l s . ( P l a t e X ) . The basement membrane i n these cases appears to remain i n t a c t . The,endothelial c e l l s l i n i n g the blood v e s s e l s are c l e a r l y evident i n a l l cases. Numbers of lymphocytes are present i n almost a l l p o r t i o n s and depths of the e p i t h e l i u m and i n the s u b e p i t h e l i a l t i s s u e . They may occur i n groups or, as i s more usual, s i n g l y . The t e e t h . The teeth, as stated (page 14), are arranged i n two arcs, an upper and a lower, along the dental arches, and i n two s t r a i g h t converging rows on the prevomers. In places along the jaws and over the prevomers, patches of e p i t h e l i a l c e l l s form an enamel organ covering a c o n i c a l p a p i l l a of connective t i s s u e . From t h i s a s s o c i a t i o n the t e e t h develop and project an enamel covered p o r t i o n s l i g h t l y above the 29 surrounding s t r a t i f i e d squamous epithelium. ( P l a t e XV). The development of the enamel and dentine f o l l o w s a sequence s i m i l a r to p l a c o i d s c a l e formation; the enamel a r i s i n g from ectodermal ameloblasts and the dentine from mesodermal odontoblasts (Walter, '40). However, instead of having a basal p l a t e buried i n the underlying connective t i s s u e l i k e p l a c o i d s c a l e s , the base of each o f the c o n i c a l teeth i s i n t i m a t e l y associated w i t h a shallow p i t i n the underlying bone. ( P l a t e XV). Around the dentine of the basal region of the tooth, through a c t i v i t y of neighbouring mesenchymal c e l l s , a cement l a y e r i s deposited which fuses the tooth to the bone of the jaw (Walter* '40). The d e n t a l s t r u c t u r e s of amphibian teeth are compara-t i v e l y s o f t and no d i f f i c u l t y i s experienced i n s e c t i o n i n g the whole tooth. The w a l l s of the d i g e s t i v e t r a c t . From the oesophagus p o s t e r i o r l y t h i s t r a c t forms a continuous tube whose w a l l throughout i t s e n t i r e length has many c h a r a c t e r i s t i c s i n common. Thus the w a l l i n a l l i t s p o r t i o n s c o n s i s t s of four coats which, from w i t h i n outward, are r e s p e c t i v e l y known as the mucous, submucous, muscular, and f i b r o s e r o u s . The mucous coat. The mucosa d i f f e r s i n each part of the t r a c t and w i l l be described separately. 30 The submucous coat. The* submucosa c o n s i s t s of a l a y e r of a r e o l a r connective t i s s u e which f i r m l y u n i t e s the mucous and the muscular coats. Throughout the t r a c t no d i s t i n c t i v e d i f f e r e n c e s are found i n t h i s coat. The muscular coat. The muscularis i s divided i n t o two layers of smooth muscle: an inner c i r c u l a r l a y e r and an outer l o n g i t u d i n a l l a y e r . In the oesophagus the c i r c u l a r l a y e r i s w e l l developed but the l o n g i t u d i n a l l a y e r c o n s i s t s only of scattered i n d i v i d -u a l strands. In the stomach a more d e f i n i t e l o n g i t u d i n a l coat i s present. As the p y l o r i s i s approached the c i r c u l a r coat becomes increased i n t h i c k n e s s w h i l e the l o n g i t u d i n a l l a y e r remains approximately constant. At the sphincter the c i r c u l a r l a y e r t h i n s abruptly to form, w i t h the l o n g i t u d i n a l l a y e r , corresponding coats i n the duodenum. Proceeding p o s t e r i o r l y from the duodenum the muscularis of the i n t e s t i n e becomes p r o g r e s s i v e l y t h i n n e r but j u s t before the colon i s reached a s l i g h t t h i c k e n i n g o f the c i r c u l a r muscle occurs. In the colon both the coats are d e f i n i t e but thinner than i n any other part of the gut. F i n a l l y i n the rectum, the c i r c u l a r muscle thickens again to form the anal s p h i n c t e r . D e f i n i t e muscle coats cannot be d i s t i n g u i s h e d i n the cloaca but bundles o f both l o n g i t u d i n a l and c i r c u l a r smooth muscle are present i n the w a l l s . 31 The f i b r o s e r o u s coat. The t u n i c a f i b r o s e r o s a i s composed of f i b r o u s connec-t i v e t i s s u e covered by an e x t e r n a l serous m e s o t h e l i a l l a y e r . This coat i n v e s t s the v i s c e r a i n the p l e u r o - p e r i t o n e a l c a v i t y . I t i s continuous and apparently homogeneous along the whole tube with the exception o f the oesophagus, the a n t e r i o r two-t h i r d s of which extends beyond the p l e u r o - p e r i t o n e a l c a v i t y and therefore l a c k s the outer mesothelium. The a n t e r i o r p o r t i o n o f the oesophagus i s supported only by loose connec-t i v e t i s s u e but the remainder of the t r a c t i s supported by mesenteries. These are double sheets of peritoneum, which are continuous with the f i b r o s e r o u s coat. In the loose connective t i s s u e between the two sheets are the necessary blood v e s s e l s , nerves and lymphatics f o r the supply of the d i g e s t i v e tube. Thus the g r e a t e r part of the alimentary canal i s supported i n a kind of s l i n g which permits freedom of movement. B. The oesophagus. ( P l a t e XVI). Throughout the l e n g t h of the oesophagus the l o n g i t u d i n a l f o l d s of the e n t a l surface are clothed w i t h p s e u d o s t r a t i f i e d c i l i a t e d columnar ep i t h e l i u m . A n t e r i o r l y t h i s coat changes g r a d u a l l y to the s t r a t i f i e d e pithelium of the pharynx while p o s t e r i o r l y i t merges w i t h the simple columnar e p i t h e l i u m of the stomach. As a r u l e the c e l l s o f the oesophageal l i n i n g stand at r i g h t angles to the basement membrane, but they are often 32 found on the sides o f the f o l d s at angles of 45 degrees. Three types' of c e l l s make up t h i s epithelium: c i l i a t e d c e l l s , goblet c e l l s and spindle-shaped c e l l s . The c i l i a t e d c e l l s are t a l l and columnar i n form and contain oval n u c l e i s i t u a t e d near the middle but nevertheless i n the d i s t a l h a l f of the c e l l . The cytoplasm i s uniform and s l i g h t l y a c i d o p h i l i c . The c i l i a are anchored by a b a s a l p l a t e and under o i l immersion appear to be attached to f a i n t i n d i v i d u a l granules, the "basal granules". The basal p l a t e i s dense and s t a i n s s t r o n g l y w i t h Congo red and A n i l i n e blue. In areas where there are great numbers of goblet c e l l s the c i l i a t e d c e l l s are squeezed between them and become narrow wi t h concave w a l l s . ( P l a t e X V I I ) . The c i l i a then appear as l i t t l e t u f t s between the swollen goblet c e l l s . The l a t t e r are p l e n t i f u l but seem to vary i n numbers i n i n d i v i d u a l s . These c e l l s are d i s t i n g u i s h e d from the neigh-bouring c e l l s by the f a c t that t h e i r f r e e ends appear c l e a r e r and are more v e s i c u l a r , w h i l e t h e i r b a s a l p o r t i o n s containing the n u c l e i are narrow and more pointed. A mucigenous r e t i -culum i s evident i n the v e s i c u l a r part o f the c e l l s . The spindle c e l l s are small and do not extend to the surface. They r e s t on the basement membrane between the other c e l l s . Their n u c l e i are o v a l and t h e i r cytoplasm i s s l i g h t l y b a s o p h i l i c . These c e l l s , as w e l l as the basal n u c l e i of the goblet c e l l s , c o n t r i b u t e to the p s e u d o s t r a t i f i e d appearance of the e p i t h e l i u m . 33 Glands of the Oesophagus. ( P l a t e X V I I I ) . The greater part of the oesophagus has no m u l t i c e l l u l a r glands, but the p o r t i o n j u s t cephalad to the stomach contains tubular glands s i m i l a r to those of the stomach. Langley (Kingsbury, '94) describes the oesophageal glands i n T r i t o n of Europe as d i f f e r i n g from the glands of the a n t e r i o r part of the stomach only i n the greater number of mucous c e l l s and tubules attached to one duct. The c o n d i t i o n i s i d e n t i c a l i n T. granulosus and f o r t h i s reason the d e s c r i p t i o n of oesophageal glands i s given under "fundic glands" i n the stomach. Po i n t s concerning the oesophagus g e n e r a l l y may be considered here: (1) An oesophagus.was taken from a newt only a few hours a f t e r i t had been fed f o r the f i r s t time i n n e a r l y f i v e months. I t was f i x e d , sectioned and s t a i n e d i n the usual manner. Large numbers of m i t o t i c f i g u r e s were observed i n the epithelium, i n d i c a t i n g that extremely r a p i d d i v i s i o n and p r o l i f e r a t i o n o f c e l l s was t a k i n g place. This process seems to continue at a r a p i d r a t e f o r only a short time however, f o r i n sections made from the oesophagus of a newt s i m i l a r l y starved, and fed two days previous to k i l l i n g , no undue m i t o t i c a c t i v i t y occurred. (2) In sections from w e l l fed animals, l a r g e numbers of lymphocytes were seen invading the ridges o f the oesophagus, i n the region j u s t a n t e r i o r to the stomach. 34 (3) In starved specimens there i s an increase i n the numbers of - a c t i v e l y s e c r e t i n g goblet c e l l s i n the e p i t h e l i a l t i s s u e . 0. The stomach. The t r a n s i t i o n from oesophagus to stomach i s e a s i l y seen on the e n t a l surface i n gross s t r u c t u r e (page 15). H i s t o l o g i c a l l y the change i s more gradual, as there i s an area i n which appear both the c i l i a t e d c e l l s of the oesophagus and the n o n - c i l i a t e d c e l l s o f the stomach. The l i n i n g of the stomach i s composed of a s u p e r f i c i a l l a y e r of t a l l columnar c e l l s and associated tubular glands (described below). The s u p e r f i c i a l c e l l s are s i t u a t e d on a w e l l developed basement membrane. Covering t h e i r d i s t a l p o r t i o n s i s a c h a r a c t e r i s t i c c l e a r border, which appears l i g h t l y s t a i n e d i n r o u t i n e s e c t i o n s / This border i s muci-genous and s t a i n s s t r o n g l y with Mucicarmine or A n i l i n e blue. The c e l l s s e c r e t i n g the border have darkly s t a i n i n g oval n u c l e i l o c a t e d i n the proximal h a l f of the c e l l . The cyto-plasm i s composed of f i n e a c i d o p h i l i c granules, sharply d i f f e r e n t i a t e d from-the d i s t a l mucous border. I n d i v i d u a l c e l l s are separated from one another near the surface by l i n e s of cement substance, "terminal bars" which show c l e a r l y i n o rdinary preparations. ( P l a t e XIX). I n f o l d i n g s of the s u p e r f i c i a l l a y e r form g a s t r i c p i t s or crypts which are l i n e d w i t h the same general type of 35 epithelium. From the crypts spring the g a s t r i c glands. These glands-are surrounded by a d e l i c a t e r e t i c u l u m of lamina p r o p r i a supporting a c a p i l l a r y supply. As the number of glands i n the a n t e r i o r p o r t i o n of the stomach increase the muscularis mucosa becomes more d e f i n i t e . I t i s composed of s e v e r a l l a y e r s of l o n g i t u d i n a l f i b e r s . In the p y l o r i c p o r t i o n of the stomach i n a d d i t i o n to the l o n g i t u d i n a l f i b e r s a few inner c i r c u l a r muscle strands are present. Contrac-t i o n s of the muscularis form the low l o n g i t u d i n a l f o l d s of the stomach. The muscularis mucosa ends at the p y l o r i c s p h i n c t e r . The mucous membrane of the stomach i s d i v i d e d i n t o two major areas each c h a r a c t e r i z e d by the kind of gland which i t contains. The a n t e r i o r two-thirds, the fundic p o r t i o n , contains the fundic glands; the p o s t e r i o r t h i r d , the p y l o r i c p o r t i o n , contains the p y l o r i c glands. The fundic glands. ( P l a t e s XX and XXI). The fundic glands of T. granulosus are very numerous. They a r i s e from the bottom of the g a s t r i c p i t s and are simple or branched tubular. The neck region of the gland i s com-posed of short columnar mucous c e l l s w i t h small i r r e g u l a r l y shaped bas a l n u c l e i . In routine preparations the cytoplasm i s c l e a r except f o r a f a i n t l y s t a i n i n g mucigenous reticul u m , but i n s e c t i o n s treated w i t h A n i l i n e blue, t h i s r e t i c u l u m shows a marked a f f i n i t y f o r the blue s t a i n . From the neck the tubules of the gland extend down towards the muscularis. 36 The l i n i n g of the tubules.Is composed of pyramidal s e c r e t i n g c e l l s with 'basal n u c l e i and cytoplasm f i l l e d w i t h coarse a c i d o p h i l i c granules. This coarse g r a n u l a t i o n i s increased i n the a c t i v e l y s e c r e t i n g c e l l s . The more a n t e r i o r fundic glands are f o r the most part b i - t u b u l a r and comparatively short. Gaudad, they become simple tubules and increase i n l e n g t h . Here they are grouped more c l o s e l y together and the c l e a r mucous c e l l s are fewer i n number. In starved newts there i s an increase both i n the s i z e and numbers of the c l e a r mucous c e l l s of the fundic glands. The p y l o r i c glands. (Tl tx."t«. XX 11 ) As the d i s t a l t h i r d of the stomach i s approached the long c l o s e l y spaced tubules of the fundic glands become l e s s frequent and the smaller l e s s numerous p y l o r i c glands begin to appear. The change i s quite abrupt but there i s a narrow area i n which both types may be found. The p y l o r i c glands are o f the simple a l v e o l a r type. They have short g a s t r i c p i t s and the mucous c e l l s of the neck region are l a c k i n g . The alveolus i s l i n e d with a s i n g l e l a y e r of cuboidal c e l l s . The n u c l e i are l a r g e and f i l l a large part of the c e l l s body. The cytoplasm i s almost c l e a r and contains no granules. The p y l o r i c glands have i n some cases s t r o n g l y acido-p h i l i c mucus i n t h e i r lumens. This mucus may have been produced by the c e l l s of the glands or, as i s more l i k e l y , by the surface e p i t h e l i a l c e l l s near the neck of the gland and become lodged there. i ' 37 The p y l o r i c sphincter r e g i o n . At t h e . p y l o r i c sphincter the g a s t r i c epithelium ends abruptly and the i n t e s t i n a l e p i t h e l i u m commences. D. The small i n t e s t i n e . ( P l a t e s X X I I I , XXIV, XXV). The l o n g i t u d i n a l f o l d s of the small i n t e s t i n e are l i n e d w i t h t a l l columnar absorbing c e l l s . Scattered among these are many goblet c e l l s . A l l these c e l l s rest on a basement mem-brane below which i s a loose a r e o l a r lamina p r o p r i a not c l e a r l y separated from the submucosa. The lamina p r o p r i a supports the "glands" of the i n t e s t i n e . In the duodenum the ducts of the l i v e r and pancreas enter the lumen of the gut. Otherwise the duodenal l i n i n g i s i d e n t i c a l w i t h that o f the rest of the small i n t e s t i n e . The absorbing c e l l s are by f a r the most numerous, c h a r a c t e r i s t i c and important elements of the mucous membrane. On the c r e s t s of the f o l d s they are long and slender while i n the depressions they are much shorter. The c e l l s are packed c l o s e l y together and i n cross s e c t i o n are prismoid i n shape. Terminal bars are present but they are not as d e f i n i t e as i n the stomach. The e n t a l border of the absorbing c e l l s i s c u t i c u l a r and shows c l e a r l y defined v e r t i c a l s t r i a -tio'ns. This border i s c l e a r and r e f r a c t i v e i n appearance and s t a i n s l i g h t l y . I t i s broadest a n t e r i o r l y i n the duodenum 38 and t h i n s out considerably as the colon i s approached. ' The n u c l e i o f these c e l l s are ovoid i n shape and contain many chromatin granules. The cytoplasm i s m i l d l y a c i d o p h i l i c and s l i g h t l y g r a n u l a r . In w e l l fed specimens the presence of f a t i s e a s i l y detected by the use of Sudan IV. Goblet c e l l s occur throughout the length o f the small i n t e s t i n e but they are much more numerous i n i t s d i s t a l p a r t . They are smaller and more re g u l a r i n shape than those of the oesophagus. The n u c l e i are s i t u a t e d at the bases of the c e l l s and the contents show the c h a r a c t e r i s t i c mucigenous r e t i c u l a r s t r u c t u r e . Eosinophiles and other lymphocytes appear f r e q u e n t l y among the c e l l s o f the i n t e s t i n a l e p i t h e l i u m . Large numbers of lymphocytes accumulate at various places i n the subepi-t h e l i a l connective t i s s u e . These " d i f f u s e lymphoid" masses • / are most numerous i n the- c e n t r a l . p a r t of the tube. No d e f i n i t e lymph nodes were l o c a t e d . "Glands". ( E l a t e s XXIII and XXV).. There are no t r u e glands i n the small i n t e s t i n e of T. granulosus. Small clumps of c e l l s with no lumen or ducts are found i n the lamina p r o p r i a j u s t below the e p i t h e l i a l l a y e r . These clumps, which appear s i n g l y or i n masses, are u s u a l l y s i t u a t e d i n the depressions between the f o l d s but are often l o c a t e d i n the l a t e r a l surface of the f o l d s . They are composed of small i r r e g u l a r l y cuboidal c e l l s with d a r k l y s t a i n i n g s p h e r i c a l n u c l e i and c l e a r cytoplasm. The c e l l w a l l s 39 are often d i f f i c u l t to d i s t i n g u i s h because of the crowding of the cell's-and because cytoplasmic processes between the c e l l s tend to obscure them. The basement membrane i s often depressed around one of these clumps, forming a pocket about the group of c e l l s . ( P l a t e XXV). , In v e s t i g a t i o n s by Bizzozero and Nic o l a s (Kingsbury, 194) upon T r i t o n and Salamanders throw doubt on the contention that s i m i l a r s t r u c t u r e s i n those animals are gl a n d u l a r . They saw no lumen and assumed that the ."clumps" are n i d i of young c e l l s from which the e p i t h e l i u m i s produced. These clumps o f c e l l s i n T r i t o n are regarded by Kings-bury as p h y l o g e n e t i c a l l y i d e n t i c a l w i t h the crypts of higher forms. A p e c u l i a r feature of a l i m i t e d area of the small i n -t e s t i n e j u s t p o s t e r i o r to the duodenum i s the presence of patches o f r o d - l i k e s t r u c t u r e s found upon the surface of the c u t i c u l a r border. ( P l a t e XXIV). In some places they appear s i m i l a r to c i l i a and might e a s i l y be mistaken f o r them. They d i f f e r from c i l i a however i n s e v e r a l respects: (1) They are not attached to the c e l l s by means of the basal granules u s u a l l y associated w i t h c i l i a and while they are g e n e r a l l y i n a p p o s i t i o n to the surface they are sometimes e n t i r e l y separate from i t . (2) They are much t h i c k e r than true c i l i a and vary i n density being darker p r o x i m a l l y and l i g h t e r d i s t a l l y . They 40 appear almost of the same consistency as the mucus secreted by goblet c e l l s but they are not a f f e c t e d by mucus s t a i n s . No s a t i s f a c t o r y explanation f o r the formation of these s t r u c t u r e s can be given. In the p o s t e r i o r p o r t i o n o f the small i n t e s t i n e the simple e p i t h e l i u m ends abruptly at the sphincter (page go) and i s followed by the s t r a t i f i e d e p i t h e l i u m o f the colon. The "glands" of the small i n t e s t i n e extend a short distance beyond t h i s c o n s t r i c t i o n . I 'v- •>'•'' I' . I . 41 E. The larg e i n t e s t i n e . The colon:. ( P l a t e XXVI). The colon i s l i n e d with s t r a t i f i e d epithelium about 4 to 6 c e l l s i n thickness. The outer l a y e r i s made up of t a l l slender columnar c e l l s and goblet c e l l s . The cytoplasm of the columnar c e l l s i s f i n e l y granular and the basal n u c l e i are oval and l i g h t s t a i n i n g . D i s t a l l y these c e l l s are covered w i t h a t h i n c u t i c u l a r border. The term i n a l bars are poorly developed and are seen only when the t i s s u e has been treated with s i l v e r impregnation methods. Goblet c e l l s are very numerous and la r g e i n s i z e . They are s i m i l a r i n form and s t a i n i n g p r o p e r t i e s to the other goblet c e l l s of the gut. The c e l l s o f the deeper l a y e r s are r e l a t i v e l y small and cuboidal i n shape. They have a c e n t r a l s p h e r i c a l nucleus f and almost c l e a r cytoplasm. The deepest l a y e r of these c e l l s i s r e g u l a r l y arranged on the basement membrane. In the ep i t h e l i u m of the colon, p a r t i c u l a r l y i n t i s s u e taken from w e l l fed specimens, there i s much evidence of c e l l u l a r breakdown. The c u t i c u l a r border i s o f t e n disrupted by the sloughing of c e l l u l a r debris i n which dense nuclear p a r t i c l e s occur. These p a r t i c l e s , as w e l l as much c e l l residue are a l s o evident deeper i n the mucous l a y e r . The p a r t i c l e s s t a i n a deep blue w i t h haematoxylin and t h e i r numbers i n d i c a t e that many c e l l s are i n the process of d i s i n t e g r a t i o n . Their shapes are i r r e g u l a r and t h e i r s i z e s vary from small densely 42 s t a i n i n g chromatin knots to l a r g e r l e s s d a r k l y s t a i n i n g nude ar fragmen t s. Some signs o f c e l l u l a r waste are evident i n the small i n t e s t i n e but are not as marked as i n the colon. Many lymphocytes are present i n the c o l o n i c mucosa but t h e i r numbers are l e s s than those of the small i n t e s t i n e . At i t s caudal end the s a c - l i k e colon narrows abruptly .and the number of goblet c e l l s i n the mucous membrane increases Accompanying t h i s increase i s a gradual t h i n n i n g o f the epithelium. ( P l a t e XXVII). The rectum. ( P l a t e XXVIII). The e p i t h e l i u m of the f o l d s o f the rectum i s s t r a t i f i e d and 2 to 3 c e l l s i n t h i c k n e s s . The e n t a l l a y e r o f t h i s l i n i n g i s composed almost e n t i r e l y of goblet c e l l s i n the swollen s e c r e t i n g c o n d i t i o n . The deeper l a y e r s are composed of cuboidal c e l l s l i k e those of the colon. The goblet c e l l s are t y p i c a l of those found elsewhere i n the i n t e s t i n e except that t h e i r n u c l e i are l a r g e r and s t a i n more l i g h t l y . This, region i s the l a s t true chamber of the d i g e s t i v e t r a c t . The c l o a c a l chamber which succeeds i t i s more c l o s e l y associated with the f u n c t i o n s of the u r i n a r y and g e n i t a l organs but i s described here because, obviously, the excreta of the t r a c t must pass through i t to reach the outside. 43 F. The cloaca. The male cloaca. The h i s t o l o g y of the c l o a c a l l i n i n g w i l l be considered i n sequence, passing from the rectum, down the c l o a c a l tube to the c l o a c a l chamber,and from thence to the outside. (a) The c l o a c a l tube. The swollen goblet c e l l s of the rectum end abruptly at the anus and are followed by the s t r a t i f i e d cuboidal epithelium 2 to 3 c e l l s i n thickness, which l i n e s the a n t e r i o r t h i r d of the c l o a c a l tube and the o r i f i c e of the bladder. As stated (page 18} l o n g i t u d i n a l f o l d s s i m i l a r to those of the rectum mark the w a l l s . Three or 4 mm. p o s t e r i o r to the anus, the ducts of the p e l v i c glands enter the tube on the t i p s of small p a p i l l a e s i t u a t e d on i t s dorsal s u r f a c e . At t h i s point, on the c r e s t s o f the l o n g i t u d i n a l f o l d s , the cuboidal e p i -thelium becomes replaced by t a l l , s i m p l e columnar c i l i a t e d epithelium. ( P l a t e XXIX). Farther caudad these c i l i a t e d c e l l s become shorter and t h e i r d i s t r i b u t i o n more general u n t i l f i n a l l y they merge w i t h the low columnar c i l i a t e d e p i t h e l i u m of the main part of the c l o a c a . As the tube enters the c l o a c a l chamber i t receives many ducts of the abdominal gland. The openings of these ducts are not s i t u a t e d on p a p i l l a e , but a number do enter on the c r e s t s of two small l o n g i t u d i n a l f o l d s s i t u a t e d one on e i t h e r l a t e r a l w a l l of the tube. 44 (b) The c l o a c a l chamber. The main chamber and the d i v e r t i c u l u m receives the ducts of the c l o a c a l gland (page 19). These ducts enter on the f l a t t e n e d c r e s t s of the ridges and to a small extent on the c l o a c a l p a p i l l a . ( P l a t e s V I I and XXXII). The e p i t h e l i a l l i n i n g i s s t r a t i f i e d , two o r three l a y e r s of small cuboidal c e l l s being s i t u a t e d beneath the e n t a l c i l i a t e d l a y e r . At the c l o a c a l aperture, the c i l i a t e d e p i -thelium gives way to an a c i d o p h i l i c mucous s e c r e t i n g coat of t a l l simple columnar ep i t h e l i u m which l i n e s the r a d i a l f o l d s of the inner part of the c l o a c a l l i p s and the crypts of the outer f o l d s . The c r e s t s of these outer f o l d s are covered with s t r a t i f i e d epidermis which coats the r e s t o f the l i p s . The cytology o f the epithelium and glands. (1) The cuboidal epithelium. The n u c l e i are oval and contain i r r e g u l a r chromatin granules; the cytoplasm i s c l e a r . A d e f i n i t e c u t i c u l a r border i s present. (2) The c i l i a t e d c e l l s . ( P l a t e XXX). The nucleus i s l a r g e , oval and c e n t r a l l y placed and contains s e v e r a l small n u c l e o l i . The cytoplasm i s c l e a r and the c i l i a are long and w e l l defined. Basal granules from which these c i l i a a r i s e are c l e a r l y evident i n routine s e c t i o n s . (3) The mucous e p i t h e l i u m o f the c l o a c a l l i p s . The c e l l s of t h i s l a y e r have round basal n u c l e i and f i n e l y granular a c i d o p h i l i c cytoplasm. Most of the c e l l s are a c t i v e l y s e c r e t i n g and e x h i b i t a mucigenous retic u l u m . (4) The c l o a c a l gland. ( P l a t e s XXXII and XXXIII). The c l o a c a l gland,although very l a r g e , i s of the simple tubular v a r i e t y . The ducts are l i n e d with low cuboidal e p i -thelium and are f o r the most part long and s t r a i g h t . The tubules, which are also s t r a i g h t and unbranched, are l i n e d w ith a s i n g l e l a y e r of cubo-columnar c e l l s . The n u c l e i of these c e l l s are i r r e g u l a r i n shape and densely s t a i n i n g . The cytoplasm i s f i n e l y g r a n u l a r , d i s t i n c t l y b a s o p h i l i c and shows a w e l l developed mucigenous reticulum. The c e l l w a l l s are not c l e a r l y defined. The c e l l s frequently merge with the s e c r e t i o n i n the lumen which appears i d e n t i c a l to the cyto-plasm. This s e c r e t i o n occurs i n great quantity i n the lumens of the tubules and ducts and i s often found i n the lumen o f the cloaca i t s e l f . (5) The abdominal gland. ( P l a t e XXXI). This gland i s also simple t u b u l a r . The ducts are s i m i l a r i n s i z e and general s t r u c t u r e to those of the c l o a c a l gland. A n t e r i o r l y they merge w i t h the s e c r e t i n g tubules of the gland while p o s t e r i o r l y they make sharp r i g h t angle turns and empty into the c a v i t y of the c l o a c a l tube as already described (page 19). The secretory tubules are long and i r r e g u l a r l y o o i l e d . The pyramidal s e c r e t i n g c e l l s l i n i n g these tubules have a basal s p h e r i c a l nucleus, surrounded by f i n e l y granular 46 cytoplasm. The d i s t a l two-thirds of the c e l l s are f i l l e d ( P l a t e XXXI). with coarse a c i d o p h i l i c (non a c i d s o l u b l e ) granules./Masses of these granules are also found i n the lumen o f the tubules and ducts. Demilunar c e l l s occur f r e q u e n t l y between the bases of the se c r e t i n g c e l l s . (6) The p e l v i c gland. ( P l a t e XXIX). The p e l v i c gland i s of simple tubular type. I t i s small and i t s ducts and secr e t i n g tubules are short. The ducts are l i n e d with low cuboidal e p i t h e l i u m While the tubules are l i n e d w i t h pyramidal secreting c e l l s . These l a t t e r have round basal n u c l e i and non-granular b a s o p h i l i c cytoplasm. They appear very l i k e the c e l l s of the l i n g u a l gland f o r a mucigenous r e t i c u l u m i s " c l e a r l y shown and the c e l l s are ob-v i o u s l y mucus s e c r e t i n g . Kingsbury ( T96) makes the f o l l o w i n g general statement: "There i s l i t t l e doubt now but that, as stated by Heidenhain and Z e l l e r , these glands, opening.upon the cloaca, discharge a s e c r e t i o n which c o n s t i t u t e s the body of the spermatophore, forming thus a base to give support on i t s summit to the zoosperms." Leydig ('92) sought to homologize these glands w i t h the prostate of mammals. Although there i s some f u n c t i o n a l s i m i l a r i t y , F r a n c i s ('34) b e l i e v e s homology to be doubtful. 47 The female cloaca. ( P l a t e XXXIV). The c a v i t y of the female cloaca i s l i n e d with s t r a t i -f i e d cuboidal epithelium, 2 to 4 c e l l s i n depth. The n u c l e i are large and i r r e g u l a r i n shape and the cytoplasm i s c l e a r and non-staining. A c u t i c u l a r n o n - s t r i a t e d border i s present. The only r e p r e s e n t a t i v e s of the glands so g r e a t l y developed i n the male are the comparatively simple spermathecae ( u s u a l l y considered to be the homologue of the male p e l v i c gland, F r a n c i s , '34) and the rudimentary t u b u l i found sur-rounding the c l o a c a l opening and a l s o i n a postero-dorsal p o s i t i o n . Tubules of t h i s type were found by Heidenhain i n T r i t o n and described as homologous to the abdominal gland. The spermathecae are b l i n d sacs l i n e d with a s i n g l e l a y e r of cuboidal epithelium. They are flask-shaped i n form, that i s , enlarged towards the b l i n d end and c o n s t r i c t e d towards the neck. These tubules open i n two l a t e r a l groups ; i n the d o r s a l side of the cloaca immediately a n t e r i o r to the openings of the u r e t e r s . Numbers of pigment c e l l s occur i n the connective t i s s u e surrounding the tubules. The tubules of the rudimentary gland are l i n e d with simple columnar epith e l i u m w i t h a basal nucleus and a granular, l i g h t s t a i n i n g cytoplasm. In the a n t e r i o r t h i r d o f the c l o a c a l tube of the male the c l o a c a l epithelium c l o s e l y resembles that of the female. Gaudad, the c l o a c a l epithelium of the male becomes c i l i a t e d , but no c i l i a occur at any place on the c l o a c a l e p i t h e l i u m of the female. 48 No goblet c e l l s are found i n e i t h e r the male or female cloacas. Associated Glands. ( P l a t e XXXV). In any d e s c r i p t i o n of the d i g e s t i v e t r a c t , the study would not be complete without a d e s c r i p t i o n of the associated glands, the l i v e r and pancreas. G. The l i v e r . ( P l a t e s XXXVI, XXXVII, XXXVIII). To f u l l y understand the s t r u c t u r e of the l i v e r i t s embryologieal development must be b r i e f l y considered. The l i v e r a r i s e s as a d i v e r t i c u l u m of the fore-gut which subse-quently d i f f e r e n t i a t e s i n t o the c y s t i c duct and the b i l e ducts. A part of t h i s primative d i v e r t i c u l u m f u r t h e r p r o l i f e r a t e s to form the f u n c t i o n i n g s e c r e t o r y u n i t s , the hepatic c e l l s (Mann, Cowdry, '28). Coincident with the r a p i d c e l l pro-l i f e r a t i o n i s the development of s i n u s o i d a l c i r c u l a t i o n . The v i t e l l i n e veins become Involved i n the. extensive •growth of the hepatic c e l l s and thus these c e l l s are associated on the one hand with the sinusoids of e n d o t h e l i a l o r i g i n and on the other hand with the b i l e c a p i l l a r i e s which are continuous w i t h the main b i l e ducts. In Urodeles the l i v e r i s a branched tubu l a r gland. The tubules c o n s i s t of double rows or cords of hepatic c e l l s . They apparently never have a w a l l o f more than three c e l l s i n thickness (Jordan, '31). The lumens of the tubules are narrow 49 channels, c a l l e d b i l e c a p i l l a r i e s , j o i n e d by grooves, the b i l e c a n i c u l i , formed between the a d j o i n i n g faces of the hepatic c e l l s . The b i l e c a p i l l a r i e s empty i n t o the smallest b i l e ducts l i n e d by low cuboidal epithelium. As the ducts increase i n s i z e the e p i t h e l i u m becomes t a l l e r and the w a l l s are invaded by a muscularis. The main duct and i t s branches -•••have a columnar e p i t h e l i a l l i n i n g and a d e f i n i t e muscularis of c i r c u l a r smooth muscle. Each columnar c e l l has a round basal nucleus and c l e a r cytoplasm except f o r an a c i d o p h i l i c mucous accumulation i n i t s d i s t a l t h i r d . The hepatic c e l l s are hexagonal i n shape, i n cross s e c t i o n , and more or l e s s pyramidal i n shape i n l o n g i t u d i n a l s e c t i o n ; the proximal base r e s t i n g on the e p i t h e l i u m of the v a s c u l a r channel while the apex i s d i r e c t e d towards the lumen, the b i l e c a p i l l a r y . ( P l a t e XXxv//) These c e l l s have round c e n t r a l l y placed n u c l e i which contain a pronounced chromatin r e t i c u l u m and s e v e r a l n u c l e o l i . In routine sections the cytoplasm has numerous small and a few l a r g e c l e a r areas among which the f i n e l y g r a n u l a r a c i d o p h i l i c cytoplasm forms a network... That these c l e a r areas contain f a t s can be shown by c u t t i n g frozen s e c t i o n s and s t a i n i n g w i t h Sudan IV. ( P l a t e .23X7111) The v a s c u l a r network, anastomosing .between the hepatic tubules, i s i n the form o f sinusoids w i t h w a l l s of endothelium and r e t i c u l a r t i s s u e . The r e t i c u l a r c e l l s are Kupffer c e l l s which,in the a c t i v e s t a t e , act as macrophages and phagocytose 50 the broken down red blood c e l l s . The n u c l e i o f these c e l l s are elongate'.in form and s t a i n densely i n routine preparations. The cytoplasm of the a c t i v e l y i n g e s t i n g c e l l s i s f i l l e d w i t h dark granules of blood pigment. In the i n a c t i v e s t a t e they appear s i m i l a r to the f l a t c e l l s of the endothelium. In T_j_ granulosus the bulk of the blood pigment i s massed i n the sinusoids but some may be located i n the Kupffer c e l l s and the hepatic c e l l s . ( P l a t e XXXYIII). In the sinusoids i t i s composed of larg e y e l l o w i s h globules and small dark brown granules. The Kupffer c e l l s ingest t h i s m a t e r i a l and reduce i t a l l to the co n d i t i o n of minute dark brown granules. From the Xupffer c e l l s the pigment i s t r a n s f e r r e d d i r e c t to c e r t a i n of the hepatic c e l l s , where i t may occur i n q u a n t i t i e s l a r g e enough t o make the whole c e l l appear dark brown. The amount of pigment v a r i e s i n i n d i v i d u a l s and with the seasons of the year. Large amounts are present j u s t before the breeding season i n the spring and l e s s e r amounts i n the summer and f a l l . Jordan ('31), i n h i s work on "The pigment of the l i v e r c e l l s of Urodeles" has made an i n t e n s i v e study of the c o n d i t i o n i n T_j_ viredescens. The condition i n T. granulosus i s very s i m i l a r to that o f T^ viredescens. Many lymphocytes and granulocytes, as w e l l as the usual red blood c e l l s , are found f r e e i n the s i n u s o i d a l spaces. 51 The capsular and sub-capsular regions. The l i v e r i s enclosed i n a t h i n connective t i s s u e capsule which i s covered by a l a y e r of mesothelium. From t h i s capsule f i n e traveculae branch into the substance of the l i v e r and penetrate to a l l i t s parts. This f i b r o u s frame-work which supports the hepatic c e l l s and the blood vessels supplying the organ, i s composed mainly of collagenous f i b e r s . Immediately below the capsule i s a l a y e r o f densely s t a i n i n g c e l l s , the subcapsular region. ( P l a t e XXXVI). This region, which v a r i e s from 5 to 10 c e l l s i n thickness, i s lymphogranuloeytopeietic. N e u t r o p h i l i c and e o s i n o p h i l i c granulocytes predominate, but many u n d i f f e r e n t i a t e d lymphocytes are present. A considerable amount of c e l l d i v i s i o n i s evident i n the l a y e r , i n d i c a t i n g r a p i d p r o l i f e r a t i o n of the lymphatic c e l l s . In the l i v e r s o f two of the specimens p a r a s i t i z e d by round worms i n the small i n t e s t i n e , a marked increase i n the numbers of eosinophiles i n the subcapsular region was observed. Below the subcapsular region i s the main bulk of l i v e r t i s s u e . 52 H. The pancreas. ( P l a t e XXXIX). The pancreas i s a compound branched a l v e o l a r gland. The main excretory ducts (which may enter e i t h e r the common b i l e duct or the duodenum, page 20) are subdivided i n t o i n t e r lobar and i n t e r l o b u l a r ducts, and are l i n e d with epithelium s i m i l a r to that of the b i l e ducts. These ducts i n turn sub-d i v i d e i n t o smaller i n t e r c a l l a r y ducts which are very slender tubules l i n e d with f l a t t e n e d epithelium. Small ductules extend from these i n t o the secretory a c i n i and are represented there by the centro-acinose c e l l s . The e n t i r e gland i s enclosed i n a very t h i n connective t i s s u e sheath whose branches form the supporting r e t i c u l a r s t r u c t u r e about the ducts and a c i n i . Many blood c a p i l l a r i e s are located i n t h i s loose connective t i s s u e . The a c i n i of the pancreas possess an i r r e g u l a r tubular form w i t h frequent a l v e o l a r d i l a t a t i o n s . The s e c r e t i n g c e l l s are i r r e g u l a r columnar or pyramidal i n shape. The d i s t a l end of the c e l l contains round, r e f r a c t i v e , a c i d o p h i l i c zymogen granules, w h i l e the proximal t h i r d of the c e l l contains a nucleus surrounded by very f i n e granular b a s o p h i l i c cyto-plasm. The nucleus I s g e n e r a l l y s p h e r i c a l and contains one larg e nucleolus although two are not uncommon. Centro-acinose c e l l s w i t h smaller darker n u c l e i and more homogeneous acido-p h i l i c cytoplasm are found f r e q u e n t l y i n the lumen of sections across the j u n c t i o n w i t h the secretory duct. In the i n t e r - a c i n o s e t i s s u e , c o l l e c t i o n s of polyhedral 53 c e l l s , the I s l e t s of Langernans, are located. Their cyto-plasm i s c l e a r or contains f i n e a c i d o p h i l i c grannies i n routine s e c t i o n s , but s p e c i a l techniques (Lane, '07), such as Goodpasture's Eosin-Methyline Blue, demonstrate c h a r a c t e r i s t i c e o s i n o p h i l i c and b a s o p h i l i c granular content i n d i c a t i n g several c e l l types. The pancreatic t i s s u e of amphibians has been considered so e x t e n s i v e l y by others (Lane, '07, Saguchi, '£0 and Janes, '34, '37, ' 38 ) that f u r t h e r e l a b o r a t i o n here i s unnecessary. 54 V I I . .SUMMARY. The h i s t o l o g i c a l s t r u c t u r e of the alimentary canal of T. granulosus has been considered and a b r i e f d e s c r i p t i o n of the l i v e r and pancreas given. Emphasis i s placed.on the f o l l o w i n g p o i n t s : 1. The mouth c a v i t y contains no s a l i v a r y glands; the tongue i s small and of a p r i m i t i v e nature. The epithelium of the o r a l c a v i t y i s h i g h l y v a s c u l a r . 2. The pharynx i s r e l a t i v e l y u n d i f f e r e n t i a t e d , i . e . , there i s no naso-pharynx. The pharyngeal epithelium i s also h i g h l y v a s c u l a r . 3. The oesophagus has no m u l t i - c e l l u l a r glands entering i n t o i t except i n the extreme caudal p o r t i o n . 4. The stomach may be d i v i d e d i n t o two portions by v i r t u e of the type of glands s i t u a t e d i n the mucosa; a l a r g e r a n t e r i o r f u n d i c p o r t i o n and a smaller p o s t e r i o r p y l o r i c p o r t i o n . 5. The.small i n t e s t i n e has no true m u l t i - c e l l u l a r glands, but r e c e i v e s a n t e r i o r l y the ducts of the l i v e r and pancreas. 6. The large i n t e s t i n e e x h i b i t s a marked increase i n the numbers of goblet c e l l s i n the e p i t h e l i a l l i n i n g . 7. The cloaca of the male and the female d i f f e r consider-ably. That of the male has a c i l i a t e d e p i t h e l i u m and i s surrounded by h i g h l y developed glands. The female cloaca e n t i r e l y l a c k s c i l i a , and i t s glands are i n a rudimentary, almost non-functional s t a t e . 55 8. The l i v e r i s a branched tubular gland and shows none of the l o b u l a r s t r u c t u r e found i n higher v e r t e b r a t e s . I t s subcapsular region produces lymphocytes and e o s i n o p h i l i c and n e u t r o p h i l i c granulocytes. 9. The pancreas i s very s i m i l a r i n s t r u c t u r e to that of higher v e r t e b r a t e s . Both the exocrine s e c r e t i n g a c i n i and the endocrine I s l e t s of Langerhans are present. 10. Goblet c e l l s are found i n a l l parts of the alimentary canal except i n the stomach and i n the cloaca. 56 Bibliography. The .following references have a d i r e c t bearing on the preceding work. Those not a v a i l a b l e to the w r i t e r are marked "Bensley S.H. (1900). The oesophageal glands of Upodela. Bio . B u l l . , V o l . 21, pp. 87-104. Bensley R.R. (1928). The g a s t r i c glands. S p e c i a l Cytology (Cowdry), V o l . I, pp. 137-167. "Bizzozero G. and N i c o l a s A. (1880). In Kingsbury (1894). "Edelmann (1889). Vergleichend Anatomische uber eine besondere Region der Magenschleimhaut. Deut. Ztschr. f. Theirmeid, V o l . XV, p. 165. "Ernst M. (1930). Zur Entwicfelungtechichte des Vordischarmes . Der Amphibien* Abst. Anat. u. Ontog. Ti e r e . , V o l . L I I , p. 3. F i t c h H.S. (1938). An o l d e r name f o r T r i t u r u s s i m i l a n s Twitty. Copeia, No. 3, Sept. 24, pp. 148-149. Fra n c i s . E.T.B. (1934,). The Anatomy of the Salamander. Oxford Press. "Goldsmith J.B. and Beams H.W. (1929). A study o f the i n t e s t i n a l glands of some Urodeles. Amer. Miero. S o c , V o l . XLVIII, pp. 292-301. "Hardy G.A. (1926). Amphibia of B.C. . Rept. Prov. Mus. Nat. H i s t . B.C., V o l . CXXXVIII, "Heidenhain M. (1890). Beitrage zur Kenntnis der Topographie und H i s t o l o g i e der Kloake. Arch. f. Mikr. Anat., V o l . XXXV, pp. 173-274. 57 Janes R.G. (1934). H i s t o l o g i c a l changes i n the alimentary-t r a c t and pancreas of Anuran larvae during i n v o l u t i o n . Jour. Exp. Zoo., V o l . LXVII, Jan., pp. 73-93. (1937) . Studies on the amphibian d i g e s t i v e t r a c t . I I . The comparative h i s t o l o g y of the pancreas f o l l o w i n g e a r l y l a r v a l development i n c e r t a i n species of Anura. Jour. Morph., V o l . LXI, D e c , pp. 581-613. (1938) . I I I . The o r i g i n and development of pan-c r e a t i c i s l a n d s i n c e r t a i n species of Anurans. Jour. Morph., Y o l . LXII, May, pp. 375-393. Jordan H.E. and Beams H.W. (1930). Hepatectomy i n the Salamander with s p e c i a l reference to hemo-p o i e s i s and cytology of the l i v e r remnant. Proa. Soc. Exp. Bi o . and Med., Y o l . XXVIII, pp. 181-184. Jordan H.E. and Speid e l CO. (1930). The hemocytopoietic e f f e c t of splenectomy i n the salamander, T r i t u r u s viredescens. Amer. Jour. Anat., V o l . XLVI, No. 1, J u l y 15, pp. 55-90. Jordan H.E. (1931). The pigment content of the l i v e r c e l l s of Urodeles. Anat. R e c , V o l . XLVIII, No. 2, Feb. 25, pp. 351-365. 58 " K a l l i u s E. (1901). Beitrage zur Entwicklung der Zunge. - •. I . T h e i l : Amphibien und R e p t i l i e n . Anat. Heft., V o l . XVI, pp. 533-760. Kingsbury B.F. (1894). The h i s t o l o g i c a l s t r u c t u r e of the enteron of Necturus maculatus. Pro. Amer. Micro. S o c , V o l . XLI, pp. 19-65. (1896). Spermatheca and methods of f e r t i l i -z a t i o n i n some American newts and salamanders. Pro. Amer. Micro. S o c , V o l . XVII, pp. 261-304. "Kingsbury B.I1. (1912). Amphibian t o n s i l s . Anat. Anz., V o l . X L I I , pp. 593-612. Lane (1907). The c y t o l o g i c a l c h a r a c t e r i s t i c s of the areas of Langerhans. Amer. Jour. Anat., V o l . V I I , pp. 409-422. "Langley J.N. (1881). On the h i s t o l o g y and physiology of pepsin forming glands. Trans. Roy. Soc. Lond., V o l . 172, pp. 663-711. "Leydig (1892). Receptaculum seminis der Urodelen. Zoo. An. Jahrg., V o l . XV, Sec. 5, pp. 309-312. Noble G.K. (1931). Biology of the Amphibia. New York. Saguchi S (1920). Glandular c e l l s of the frog's pancreas. Amer. Jour. Anat., V o l . XXVI, Jan., pp. 347-423. 11920). C y t o l o g i c a l studies of Langerhans c e l l s . Amer. Jour. Anat., V o l . XXVIII., Nov., pp. 1-59. " S k i l t o n (1849). Salamandra ( T r i t o n ) Granulosa. Amer. Jour. S c i . A r t s , V o l . V I I , Ser. 2, p. 202. 5 9 Smith G.M. ( 1 9 2 7 ) . The d e t a i l e d anatomy of T r i t u r u s torosus. Roy. Soo. Can., V o l . XXI, Sec. 5 , pp. 4 5 1 - 4 8 4 . Stejneger L. and Thomas B. ( 1 9 3 9 ) . T r i t u r u s granulosus S k i l t o n . Check L i s t N. Amer. Amph. Rept. Twitty V.C. ( 1 9 3 5 ) . Two new species of T r i t u r u s from C a l i f o r n i a . Copeia No. 2 , J u l y 1 6 , pp. 7 6 . Texts f o r general reference. Bensley R.R. and Bensley S.II. ( 1 9 3 8 ) . A handbook of h i s t o l o g i c a l and c y t o l o g i c a l technique. Chi. Press. Cowdry E.V. ( 1 9 2 8 ) . S p e c i a l Cytology, Vols. I and I I . Hoeber. Inc. ( 1 9 3 8 ) . A textbook of h i s t o l o g y . Lea and Febiger Guyer M . j T . ( 1 9 3 6 ) . Animal Micrology. Univ. Chicago Press. Jordan H.E. ( 1 9 3 7 ) . A textbook of h i s t o l o g y . D. Appleton Inc K r a j i a n A.A. ( 1 9 3 8 ) . H i s t o l o g i c a l technique. P r i v a t e P u b l i c a t i o n . M a l l o r y F.B. ( 1 9 3 8 ) . P a t h o l o g i c a l Technique. Saunders. Maximow A.A. and Bloom W . ( 1 9 3 9 ) . A textbook of h i s t o l o g y . Saunders* Noble G.K. ( 1 9 3 0 ) . Biology of the Amphibia. McGraw-Hill. Walter H.E. ( 1 9 4 0 ) . Biology of the Vertebrates. Macmillan. P l a t . I T n t urj% o^ran\)I ibus Male, and Female 5k. l t on. (d Hit brocxd Hud , 5lmoil til "ikih, well Ac«t: lobick tai l - • f in o £ t k t male. ara.Kjlft.r •&kih 0-f the ftMA.lt . Egg 1- caosi the li»*ilet\ abdomen. X I ram ol D i g e s t i v e . " T r a c t VVnfm./ a. $ fact. Trt tarn oil nart'i. .?Koiir yn K. .Tongue. .Liver - j / . Pyloric slomixtk ?anc reas _ _ DuodxinuK\ Small liat^ime Col cm urn A 2. ( 4 pro*. " P l a t e m / O X EJ3i + t\a.lici.l lining 5 J b w\uco six F'l b TO - 'blLI'OH. ott. T hi. longiiuAittil rolcU. X 3 0 - ^>uii mucosa. -Civ-cukr Molclt Iciyar X30 ? l a t i X C l r o l ^ lnLcVioh 0-f fundus o ? i l i t 5 i omacl\. &.VS.V-GlartcLo lar «JMot. Muscularis mucoid 5ubwvjcos<x Circular muscln. layir Lo A^ifudiniA (aytr Filora -<;«.ros<x. Noil . l U low uJlcU-tntsKlA W i s Or- r-uaat X3o CroW "bcc-hor, o-f ?y /onc Stowo-ck — Circular rnoscd (a.yir fjre.a.^ (y increase „_ Loin tti4udmiL.l Wore war (via G lala iiillar arttt Muscularis i»ijcoso>. X 3 0 P l a t e YI Cro<bS Section o-f tint Small Intestine-, E jjitlni.1 tal layir "Glands" 5ub Mucosa. Circular rvwsxlt layir Longitudinal layer Note.. The. vwe.ll (A.tv-«/o^ xtci folds, of the mucosa. Crot)^ sec t ion of the. Colon 5t rail-find elpittitlicd layer 5ulo wvu COsa C i r c u l u r tausck layer l_on<y {u dmal layer Note . I he rdaliiftlj tjtdbiltai Surface.. n o s i d i o n o-? "tkt Male CI oata .loWts o{ flic Atj g /and • uic q/aittA — Cloacal "tube It* o"t 'KM. CloaxoJ a land '?°«°OH _..Tk ClOatol babdk Duci'j o •? "tfn. Clotuoi glanil String +(|t I » { M i :"tod«.|-Hr>. The fla./fbJj)tol fidlji*. X 50 Croet stciion b-f -He Pa^aU Cloaca X30 " P l a i t H XlO X/0 " P i a t t X O r a l f b i t h e.11 u m . Cuticjlar WoUr ... Gob \<L\ CukoiioJ calU t .'B)ttliiHnet\{ wiinbraru . RiA blooi till in tn \arg tel. C<x|) l 11 ary E n d b i k t l i a . 1 c d l Lo,hun&. propria Cajsi i L r y lull 0 f red blood ulfs. 5u |j WuCoSfc X (ZOO P l a t e H Lingual GfahdU X 200 Mole. A l l f i t t u e s bdoto (jraf-ied (not o l k t r w i H nbini) win •fixed lh B o u i i V * and bioilnik Willi Congo r i d and rf«.t*naJ0 ty /in . " P l a t e X I Lingual g l ands X200 P l a + e H E X200 • ^^^^^^^ ^ o s ^ r ' ° | r ^ a r^ °^ ^ ° ^ u t • L i . win* ^Kajfrlft K 2 0 0 T e e t h fdaderw ~T t\t i c l oderw . No"fe. +ka. e ieM. a.Ssoc.m.'i'foti Iks. Tootk uuifla MIL uni tr (yino 4>oiu. -Fully d i m lo Jitd. "too-fk j>rBJ(t^ini| dtoira i k t i j ic fkt lun • E mimt. I or gift Ds.vilo|»ir\ g too+W M«.SO dermal j>a|)< llo-Oral & Jiifks. I lUkw X 2 0 0 0 < L 5 o j)h a g COL I <L [> i t h i h u m A looo ~PI ate. TvTn ' G I txa d. ^ m f r u . extreme. caudoJ 5 1 ZTio - d i d ^ r a m o-f f l i t G a v t n t E [>l+U«. I ium TurlollC. fortiori o-f "Hu SiomOxk. Molt ildh bi-iufc I flois. ttfBuiid 1)4/4\ Cllaf rAUtaj", flick etil't SubmucoSa Muscular^ UMJCOSO. M O O VUi<L TXT F u n d t c GjlcunoU J C l e a r rnucoi/'; n e c k t i l ' ? X IOOO P l a t e X X l l Pyloric 1^oriior\ o"f the 5"ioma.ck Circular muscle Itc^cr X2O0 %i<rr\^o^, WWc// i l ooo Cnololoi call (till fhtliut* C i u m | i o-f C« ((") i n (X X1200 " P l a t e XKVf XlOO iht Colon. X 200 (Void ik 4rfh tllUrn — Ac!Ii/ t l y < i e c n l i h & (joUil t t | wM*k| it Aid, X 1 0 0 0 . Clocxca Male C l o a c a l T u b e — rabi lla c.ojrr"j~ ma a duel of ._. O i l o^e d C o U L U K K C A of Cloaco.1 Tube dot-sal ait trie (jland -•v-?- ^ tCre!ihtj faults of the Tcfu.c G/arxd noo " P l a t e Ml Ciliated fold of Ike Cloacal Tute C i l i a -|jastmiK+ mtwi bra ml X 1000 A b d X 5 0 0 " P l a t e WTl Cloaca! Glandi " P l a i t T u r n ion m — 5 km* 11 <i ee r t "tin oj 4ulsu(a o N o t * . 7 k t ? l * t c e i l ) w i t l i j>arft.r\f uJeJU a n d j - l u l a r i j i amoumf 5tcrt4ioK Ift flrta lu<*l«(V. U)a. dttt I't » A Ideas A ( 0 0 0 " P l a t e . XXX\/ Ln/ir. A/t>4 c "tkt dark jngmtni mn««5. X - - Purttrlfc^flt i l«t«r lobar 1 duffk, From d Os-i* <i<Z.c^ow aMki tuL+U 0.H X35 •^ICX+CL X X X V I P l a t e Toavii 5kouuiHc^ £&{ a * ii&lutd. U)l\k S u d a n 11/ tff kfcjoofit c.«JU . E r t l a - f l l t J l f t . 1 t a l l Sinusoid 6 l / l C6-|)l l l i r ' y l-itb i^t t i l l |ayrft.iKnLI in lon£)i{ucii«4.( sicliwi. -'Re<A blood u l l (^ / loo H i 1 5 _ _ Sub ctk.jp'jula.r r c a i o K -(lift rj/ottd ci(l5 Simps.«, tft.iM.tit tAUo, XlQQO ?lafe . M i l ^ u3 5 k oujma a c i n i . Goodl |jas"f or«'5 E o ^ n - Mefky line blot 

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