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The external morphology of AOPLUS CESTUS (Cresson), (Hymenoptera: Ichneumonidae), a parasite of the oak… Miller, Charles Douglas Fairbanks 1951

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THE: EXTERNAL MORPHOLOGY OF AOPLUS CESTUS (CRESSON), L- £~ 5 3 7 (HYMENOPTER&: ICHNEUMONIDAE), A PARASITE; OF THE OAK LOOPER AND HEMLOCK LOOPER I N B R I T I S H COLUMBIA b y CHARLES DOUGLAS FAIRBANKS M I L L E R T e c h n i c a l O f f i c e r 2, B i o l o g i c a l C o n t r o l I n v e s t i g a t i o n s L a b o r a t o r y , A THESIS SUBMITTED I N P A R T I A L FULFILMENT OF THE REQUIREMENTS FOR. THE; DEGREE OF i n t h e D e p a r t m e n t o f Z o o l o g y We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e s t a n d a r d r e q u i r e d f r o m c a n d i d a t e s f o r t h e V a n c o u v e r , B . C . MASTER OF 6 UMMJ& V d e g r e e o f MASTER OF Members o f t h e D e p a r t m e n t o f THE: UNIVERSITY OF B R I T I S H COLUMBIA A p r i l , 1951 A b s t r a c t The e x t e r n a l m o r p h o l o g y o f A o p l u s c e s t u s ( C r e s s o n ) , a n I c h n e u m o n i d p a r a s i t e o f t h e o a k l o o p e r a n d h e m l o c k l o o p e r i n B r i t i s h C o l u m b i a , i s d e s c r i b e d . A n a t t e m p t i s made t o h o m o l o g i z e t h e s t r u c t u r e s o f t h i s h i g h l y - m o d i f i e d i n s e c t w i t h t h o s e known i n more g e n e r a l i z e d i n s e c t s , i n t h e hope o f c l a r i f y i n g some q u e s t i o n s o f I c h n e u m o n i d m o r p h o l o g y w h i c h have b e e n n e g l e c t e d b y e n t o m o l o g i s t s . The t e r m i n o l o g y u s e d was s e l e c t e d f r o m a u t h o r s whose n o m e n c l a t u r e i s g e n e r a l l y a c c e p t e d b y p r e s e n t - d a y m o r p h o l o g i s t s • - i i i -I n d e x A b s t r a c t i i i I n t r o d u c t i o n 1 S t u d y a n d i t s p u r p o s e 3 E c o n o m i c p o s i t i o n 3 S y s t e m a t i c p o s i t i o n 3 A c k n o w l e d g m e n t s 4 M a t e r i a l s a n d T e c h n i q u e s 5 G e n e r a l Anatomy 6 The Head 8 E x o s k e l e t o n 8 Head s c l e r i t e s 8 E n d o s k e l e t o n 11 The t e n t o r i u m 11 The Head Appendages 12 The t r o p h i 12 The C e r v i x 15 The T h o r a x a n d E n d o s k e l e t o n 16 The p r o t h o r a x 16 The p t e r o t h o r a x 18 The m e s o t h o r a x 20 The m e t a t h o r a x 22 The L e g s 24 The l e g a r t i c u l a t i o n s 25 The W i n g s 26 The f o r e - w i n g 28 The h i n d - w i n g 29 The a x i l l a r y s c l e r i t e s 30; The Abdomen 32 The p r e g e n i t a l segments 32: The g e n i t a l segments 34 The p o s t g e n i t a l segments 34 - i -The G e n i t a l i a 34 The f e m a l e g e n i t a l i a . 35 The m a l e g e n i t a l i a 36 Summary 39 L i t e r a t u r e G i t e d 40 - i i -I n t r o d u c t i o n M o d e r n t a x o n o m i s t s g e n e r a l l y a g r e e t h a t no one c r i t e r i o n i s s a t i s -f a c t o r y f o r d e t e r m i n a t i o n o f s p e c i e s . The r o l e o f m o r p h o l o g y i n s y s t e m a -t i c s i s u n s u r p a s s e d , a n d u n t i l r e c e n t l y i t h a s b e e n t h e o n l y f u n c t i o n a l c r i t e r i o n f o r d i s t i n g u i s h i n g g r o u p s o f p l a n t s a n d a n i m a l s o f t h e h i g h e s t a n d l o w e s t c a t e g o r i e s one f r o m t h e o t h e r . A d m i t t e d l y , i t s power a s a s i n g l e means f o r i d e n t i f i c a t i o n o f s p e c i e s i s d i m i n i s h i n g due t o t h e c r i -t e r i a e v o l v i n g f r o m g e n e t i c a l , p h y s i o l o g i c a l , a n d e c o l o g i c a l s t u d i e s , b u t i t must be remembered t h a t t h e s e a r e n o t r e p l a c e m e n t s b u t s u p p l e m e n t s f o r t h e s t u d y o f m o r p h o l o g y . The i m p o r t a n c e o f t h e r o l e o f m o r p h o l o g y i n t h e p a s t i s b e s t d e s c r i b e d b y Brown (1949). He r e l a t e s : " E v e r y o n e who has s t u d i e d b i o l o g y a p p r e c i a t e s t h e c l a s s i c r o l e t h a t c o m p a r a t i v e m o r p h o l o g y h a s p l a y e d i n t h e d e v e l o p -ment o f s y s t e m a t i c b i o l o g y . S i n c e t h e e a r l i e s t t i m e s man h a s r e c o g n i z e d t h e e m p i r i c a l f a c t t h a t a n i m a l s a n d p l a n t s c a n be s o r t e d by_ m o r p h o l o g i c a l  c h a r a c t e r i s t i c s , w i t h g r e a t e r o r l e s s d i f f i c u l t y , i n t o g r o u p s t h a t c a n be c a l l e d k i n d s o r s p e c i e s , a s w e l l a s i n t o h i g h e r g r o u p s . One o f t h e mos t i m p o r t a n t f e a t u r e s o f t h e s y s t e m d e v i s e d b y L i n n a e u s i s t h e c o n c i s e m o r p h o l o g i c a l d e f i n i t i o n o f t h e s p e c i e s and o f t h e h i g h e r g r o u p s " . (The i t a l i c s a r e m i n e . ) F r o m t h i s i t c a n be s e e n t h a t m o r p h o l o g y i s i m p o r t a n t ; i n f a c t , i t s i m p o r t a n c e was a t f i r s t o v e r s t r e s s e d a n d c o n s e q u e n t l y l e d t h e s y s t e m a t i s t s t o a p u r e l y a r b i t r a r y c l a s s i f i c a t i o n o f p l a n t s a n d a n i m a l s , a n d s u b s e q u e n t l y t o a n a r b i t r a r y d e f i n i t i o n o f s p e c i e s . Though t h i s i s t r u e , t h e a u t h o r i s i n c l i n e d t o c o n c u r w i t h B r o w n (1949) when he w r i t e s , "The p l a c e o f m o r p h o l o g y i n s y s t e m a t i c s , a b u s e d a n d m i s u n d e r s t o o d i n t h e p a s t , i s b e i n g r e - e v a l u a t e d g e n e r a l l y a n d i s s e c u r e b e c a u s e o f t h e 2 empirical fact that the majority of animals can be sorted into groups that we cal l species. And without an appreciation of morphological relation-ships, one cannot easily and quickly deduce knowledge of a strange species to the benefit of a practical problem". The import of the latter statement may be realized when we examine the purpose behind the morphological study of the hymenopterous thorax by Snodgrass (19U). He states: "The gypsy moth and brown t a i l moth have been for a number of years greatly infringing on human interests and plea-sure in certain parts of New England. A most promising means of combatting them is the importation and rearing of destructive hymenopteran parasites. Students of these parasites discover that the thorax presents valuable characters for the determination and classification of species, but they are handicapped by the lack of reliable studies on the structure of the thorax among the parasitic Hymenoptera in general". Because of this lack of knowledge of the hymenopteran thorax, Snodgrass undertook the study. He found later that i t not only entailed a study of the thoraces of the parasites, but also of the lower Hymenoptera in order to obtain the homolo-gies of the more specialized group to the generalized and more primitive insects. He explains that "experience shows that no special branch of entomology can be developed properly unless based on a knowledge of the fundamental structure of insects in general". The importance of morphology as a part of present day systematics is stressed by the comments of Ferris (1928). He relates that systematic entomology is simply the study of comparative morphology with the formula-tion of conclusions as to morphological relationships, and that, though morphology has limited aims (such as attempts to correlate structure and 3 function), beyond this it is nothing but the study of the basic data of systematics. Furthermore, he points out that any systematic entomology which ignores this fact is cutting itself off from the right to be regarded as a science. Feelings such as these, expressed by men who are respected authorities in their fields of endeavour, justify and keep secure the study of morpho-logy as a science in its own right, and should convince us that, although diminishing in power as a single criterion for definition of species, i t s t i l l plays and always will play a leading role in biology. Study and its purpose. This paper is a morphological study of a parasitic hymenopterous fly belonging to a sub-family much neglected by insect taxonomists. The subject was suggested by the Canadian hymenopteran authority, G. S. Walley, whose opinion is that such a study will lay down a basis for further studies, taxonomical or morphological, of this group of insects. Economic position. Economically speaking, Aoplus cestus (Cresson) may be considered a beneficial insect. It provides a potential weapon to combat and control epidemics of the oak looper, Lambdina somniaria (Hulst), and the hemlock looper, Lambdina fiseellaria lugubrosa (Hulst), serious insect pests of two of our important forest trees. Systematic position. Aoplus cestus (Cresson) was originally described by E. T. Cresson (1878) from material collected on Vancouver Island. At this time it was placed in the genus Ichneumon. A recent revision of the classification of the Nearctic Ichneumonidae by Townes (1944), however, has placed this species in the genus Aoplus, giving i t a new combination—Aoplus cestus (Cresson). The genus Aoplus was originated, by Tischbein in 1874, but was not used for Neaatic species until 1944 at which time Ichneumon cestus Cresson and thirteen other species were referred to i t . The majority of these species (including cestus) had previously been placed in the genus Ichneu- mon (sometimes referred to as Amblyteles). The genus Ichneumon has had a complicated nomenclatorial history, but in general has been used by early authors such as Cresson, Provancher, Ashmead and Viereck for numerous species currently assigned to many of the restricted groups now placed in various tribes of the Phaeogeninae. In Townes' (1944) classification, Aoplus cestus (Cresson) is placed as follows::— Family—Ichneumonidae Sub-family—Phaeogeninae Tribe--Amblytelini Genus—Aoplus Species—cestus In this classification, the family Ichneumonidae is divided into twelve sub-families,among which Phaeogeninae stands fourth. This sub-family is composed of nine tribes, Amblytelini standing seventh. The tribe Amblyte-l i n i is subdivided into sixteen genera in which Aoplus is placed fourth, between Cratichneumon and Patroclus. Fourteen spcies of Aoplus are recog-nized in America north of Mexico. Acknowledgments The author wishes to express grateful thanks to Professor W. A. Clemens, Head of the Department of Zoology, University of British Columbia, for his permission to present this paper as partial fulfillment of the requirements for Master of Science in Agriculture degree, and to Professor G. J. Spencer, I 5 . Depar tment o f Z o o l o g y , f o r h i s d i r e c t i o n a n d c r i t i c i s m s d u r i n g t h e p r o g r e s s o f t h e w o r k . The a u t h o r w o u l d a l s o l i k e t o e x p r e s s h i s a p p r e c i a t i o n t o M r . A . B . B a i r d , H e a d , B i o l o g i c a l C o n t r o l I n v e s t i g a t i o n s U n i t , O t t a w a , a n d M r . J . H . M c L e o d , O f f i c e r - i n - C h a r g e , B i o l o g i c a l C o n t r o l I n v e s t i g a t i o n s L a b o r a t o r y , U n i v e r s i t y o f B r i t i s h C o l u m b i a , f o r a l l o w i n g h i m t o p r e p a r e t h i s w o r k i n c o n j u n c t i o n w i t h o t h e r w o r k c a r r i e d o n a t t h e V a n c o u v e r l a b o r a t o r y , a n d f o r t h e u s e o f t h i s l a b o r a t o r y ' s f a c i l i t i e s ; a n d t o M r . G . S . W a l l e y , S y s t e m a t i c U n i t , O t t a w a , f o r s u g g e s t i n g t h e p r o b l e m , f o r g i v i n g h i m i n f o r m a t i o n c o n c e r n i n g t h e s y s t e m a t i c p o s i t i o n o f t h e i n s e c t , a n d f o r r e f e r e n c e s t o l i t e r a t u r e . M a t e r i a l s a n d T e c h n i q u e s The m a t e r i a l was c o l l e c t e d i n V i c t o r i a , B . C . , i n t h e a r e a s i n f e s t e d d. b y t h e oak l o o p e r . The s p e c i m e n s s t u d i e d were c l e a r e d w i t h a 10 p e r c e n t s o l u t i o n o f p o t a s s i u m h y d r o x i d e . A l l d i s s e c t i o n s w e r e made i n 70 p e r c e n t a l c o h o l a n d g l y c e r i n . B e c a u s e o f t h e i n s e c t ' s l i g h t c o l o u r , i t was u n n e c e s s a r y t o b l e a c h o r s t a i n a n y o f t h e s k e l e t a l p a r t s . The c l e a r i n g w i t h p o t a s s i u m h y d r o x i d e was s u f f i c i e n t t o p e r m i t t h e . s t u d y o f t h e c o m p l e t e s k e l e t o n w i t h l i t t l e d i f f i c u l t y . The s k e l e t o n was e x a m i n e d t h r o u g h a L e i t z b i n o c u l a r w i t h a s q u a r e d e y e -p i e c e . The l a t t e r made i t p o s s i b l e t o d r a w t h e v a r i o u s p a r t s t o s c a l e o n s q u a r e d p a p e r f r o m w h i c h t h e i l l u s t r a t i o n s were t r a n s f e r r e d t o B r i s t o l b o a r d f o r r e p r o d u c t i o n . 6. General Anatomy Since A. cestus is an Ichneumonid, i t is typical of the suborder Glistogastra as defined by Comstock (1936). The tergum of the first abdominal segment is attached to and forms the propodeum (Fig. 16 IT) of the thorax. The second abdominal segment (Fig. 57, 58 11T) is strongly constricted. It forms a slender petiole, or waist, between the alitrunk, or wing-bearing region of the body, and the larger portion of the abdomen. This species averages in over-all length 10.5 mm. for the female, and 12 mm. for the male. The head and body are approximately 2 mm. wide. The head is as deep as i t is wide. The thorax is approximately 4 mm. long and 2.5 mm. deep. The abdomen of the male is from 1.5 mm, to 2 mm. longer than that of the. female. The integument is relatively thick, tough, and elastic, and is trans-parent when the body is cleared with potassium hydroxide. The surface is punctate and is covered with fine hair which is sometimes difficult to see except in some lights. The metanotum (Fig. 28, 29, 30 N3) and propodeum are sculptured. The latter is slightly excavated behind, and its dorsal posterior angles are bluntly spiniform (Fig, 29 IT). The sculpturing of the propodeum makes i t difficult and sometimes impossible to distinguish the lateral, central, and other propodeal areas used by inseet Systematists in their descriptions of other hymenopteran groups. The body varies from a dark to pale ferruginous colour, but the f o l -lowing parts are black:—the distal parts of the mandibles, most of the ocular sclerites, the occiput, the prosternum, the anterior and lateral surfaces of the mesonotum, most of the prepectus, the posterior margin of foveas. the mesosterntun, ^he scutellar favac, the paraptera of the metapleura, 7 t h e b a s e o f t h e p ropodeum, most o f t h e m e t a s t e r n u m , a n d t h e b a s a l o n e -q u a r t e r t o o n e - h a l f o f t h e t r u e f o u r t h a b d o m i n a l t e r g i t e . T h i s b l a c k i s a c h a r a c t e r i s t i c u s e d i n K e y s t o d i s t i n g u i s h t h i s s p e c i e s f r o m c l o s e l y r e l a t e d s p e c i e s . I n t h e s e r i e s o f s p e c i m e n s c o l l e c t e d a n d e x a m i n e d b y t h e a u t h o r , h o w e v e r , some m a l e s p e c i m e n s , p r o b a b l y t e n e r a l , l a c k e d t h i s c h a r a c -t e r ( i t i s s u s p e c t e d t h a t t h i s i s due t o c o l o u r v a r i a t i o n w i t h i n t h e s p e c i e s ) . The t r u e t h i r d a b d o m i n a l t e r g i t e b e a r s two t r a n s v e r s e , o b l i q u e , q u a d r a t e p i t s n e a r i t s a n t e r i o r m a r g i n , t h e g a s t r o - c o e l i a s d e f i n e d b y T o r r e - B u e n o (1937). The w i n g membrane i s y e l l o w i s h - h y a l i n e , a n d f o r m s a c o n t r a s t i n g b a c k g r o u n d f o r t h e b r o w n i s h v e i n s . The h i n d - w i n g s a r e much s m a l l e r t h a n t h e f o r e - w i n g s t o w h i c h t h e y a r e a t t a c h e d d u r i n g f l i g h t b y t h e h a m u l i ( F i g . 5 2 B ) . E x c e p t f o r t h e d i s t a l p o r t i o n o f t h e h i n d t i b i a e , w h i c h i s f u s c o u s , t h e l e g s a r e t h e same c o l o u r a s t h e b o d y . The h i n d l e g s a r e much l a r g e r t h a n t h e m i d d l e l e g s , w h i c h a r e a l i t t l e l a r g e r t h a n t h e f r o n t l e g s . The a n t e n n a e o f b o t h s e x e s a r e a p p r o x i m a t e l y t h e same s i z e a n d b e a r t h e same number o f s e g m e n t s . The t w e l f t h t o s e v e n t e e n t h segments a r e l i g h t e r t h a n t h e o t h e r s e g m e n t s ; i n some c a s e s t h e c o n t r a s t i s more d i s t i n c t t h a n i n o t h e r * E x c e p t f o r a s l i g h t v a r i a t i o n i n c o l o u r a n d s i z e , a n d d i f f e r e n c e s i n g e n i t a l i a , t h e m a l e a n d f e m a l e o f c e s t u s a r e a l m o s t i d e n t i c a l . F o r t h i s r e a s o n , a n d t h e f a c t t h a t o n l y a l i m i t e d s u p p l y o f f e m a l e s was a v a i l a b l e , a l l t h e i l l u s t r a t i o n s w e r e made f r o m t h e m a l e e x c e p t where o t h e r w i s e s t a t e d . 8. The Head E x o s k e l e t o n From t h e a n t e r i o r a s p e c t ( F i g . 3), t h e h e a d o f c e s t u s i s c i r c u l a r i n s h a p e . The d o r s u m i s s l i g h t l y f l a t t e n e d . The s i d e s , t h r e e - q u a r t e r s o f w h i c h a r e made u p o f t h e compound e y e s ( E ) , a r e s t r o n g l y c u r v e d a t t h e g n a t h a l r e g i o n . The h e a d i s h y p o g n a t h o u s , a c o n d i t i o n c o n s i d e r e d s p e c i a l i z e d b y W a l k e r (1932), a n d p r i m i t i v e b y S n o d g r a s s (1935). The h e a d s c l e r i t e s . M o d i f i c a t i o n o f t h e h e a d c a p s u l e o f Jju c e s t u s b y c o m p l e t e f u s i o n o f some s c l e r i t e s , a n d c h a n g e s i n p o s i t i o n a n d shape o f o t h e r s , h a s made i t i m p o s s i b l e t o l i m i t e x a c t l y t h e v a r i o u s a r e a s d e s i g n a t e d b y S n o d g r a s s (1935) i n t h e g e n e r a l i z e d i n s e c t h e a d . H o w e v e r , f o r d e s c r i p t i v e p u r p o s e s , t h e c r a n i a l r e g i o n s a r e d e f i n e d a s f o l l o w s : — -The f r o n s ( F i g . 1, 3 F R ) i s t h e n a r r o w a r e a b e t w e e n t h e a n t e n n a e s t r e t c h i n g v e n t r a l l y f r o m t h e m e d i a n o c e l l u s (MO) t o t h e c l y p e u s ( C L P ) . I t i s e x c a v a t e d b e t w e e n and a b o v e t h e a n t e n n a l s o c k e t s i n o r d e r t o a c c o m o -d a t e movement o f t h e l a r g e b a s a l a n t e n n a l segments ( B S ) . The f r o n s u s u a l l y i n c l u d e s t h e m e d i a n o c e l l u s a n d t h e a r e a i m m e d i a t e l y a r o u n d i t . The c l y p e u s ( F i g . 2, 3, 6 CLP) i s t h e s c l e r i t e i m m e d i a t e l y v e n t r a d t o t h e f r o n s . I t i s s e p a r a t e d f r o m t h e l a t t e r b y t h e p o o r l y - d e f i n e d e p i s t o m a l o r f r o n t o - c l y p e a l s u t u r e (ES) i n w h i c h a r e l o c a t e d t h e a n t e r i o r t e n t o r i a l p i t s ( A T ) , l a n d m a r k s f o r t h i s s u t u r e . The l a b r u m ( F i g . 3 6 LM) i s t h e f l a p - l i k e s c l e r i t e f l e x i b l y a t t a c h e d t o t h e v e n t r a l m a r g i n o f t h e c l y p e u s . I t s i n n e r s u r f a c e i s c o n t i n u o u s w i t h t h e i n n e r s u r f a c e o f t h e c l y p e a l r e g i o n o f t h e h e a d , o r e p i p h a r y n g e a l w a l l o f t h e p r e o r a l c a v i t y , w h i c h ends a t t h e o r a l a p e r t u r e . The p a r i e t a l s ( F i g . 2, 3, 4, 5 PRTL) a r e t h e l a t e r a l a r e a s o f t h e h e a d . Each parietal bears a large compound eye (E), a lateral ocellus (LO), and an antenna (BS). They are rather large in JL cestus» and make up a large part of the head. The vertex (Fig. 2, 4, 5 VX) is made up of the dorsal surfaces of the parietals. It is the area directly posterior to the lateral ocelli and between the compound eyes. Since the head is wide in cestus, the vertex is correspondingly large. The genae (Fig. 2, 3, 4, 5, 6 GE) are the ventral areas of the parie-tals. They are considerably reduced in Aj_ cestus due to the large compound eyes. The occipital arch (Fig. 4 OC) is a large, concave, horseshoe-shaped sclerite forming the posterior wall of the cranium. Its dorsal and lateral positions surround the small occipital foramen (FOR), the posterior ary aperture through which pass the alimenta^ canal, nerve cord, and salivary glands. It is separated from the parietals by the ridge-like occipital suture (OGS), which meets the subgenal suture a short distance from the mandible (Fig. 4, 5). The ventral areas of this sclerite are termed the postgenae in generalized insects, and are sometimes, according to Snod-grass (1935), divided from the upper part, or occiput, by a suture. In this species, the two are solidly fused, and one can only refer to the postgenal area as the ventral portion of the occipital arch. The area of the occipital arch surrounding the occipital foramen is bent posteriorly, and forms three occipital condyles (Fig. 4 OCC), one dorsal and two lateral, for articulation with the prothoracic segment. This area i s referred to by Snodgrass (1935) as the postocciput, and is usually separated from the occiput by a postoccipital suture, which is identified by the presence of 10. the posterior tentorial pits. The posterior tentorial pits (PT) are present in Aj_ cestus, but no trace of a suture separating the occiput from the postoccipital area was located. Snodgrass (1935) has referred to this suture in generalized insects as the only suture of the definite insect head that persists after fusion of the various head segments of the insect ancestor. Apparently, most of this suture is obliterated in A.  cestus, and a l l that remain are the tentorial pits. The subgenae (Fig. 4, 5 SGE) are long, narrow sclerites on the ventral edges of the occipital arch from which they are divided by subgenal sutures. They extend to the neck region where their inner margins are extended mesally, and are united in a broad hypostomal bridge (HB), which separates the labio-maxillary complex from the occipital foramen and cervical region. Bucher (1948) refers to this region in Monodontomerous dentipis Boh., an entomophagous chalcid, as the gular region, a term generally associated with a prognathous condition of the head. It should be noted that in Snodgrass's explanation of the gula, the posterior tentoral pits are always anterior to the gular region, and in his explanation of the hypo-stomal bridge these pits are always posterior to this region. Therefore, the area designated the gula by Bucher in Mj_ dentipis is more likely a hypostomal bridge. This bridge, according to Snodgrass (1935), begins in the adult Tenthredinidae as elongations of the hypostomal region of the subgenae. Therefore, i f we are to accept the fact that the Tenthredinidae are the ancestors of the higher Hymenoptera, we must refer to this region as the hypostomal bridge and not as a gula. 'The region immediately posterior to the hypostomal bridge and between the posterior tentorial pits is strengthened on each side by sclerotized interal ridges (ITR), 11. externally revealed by a darkening of the chiton. Endoskeleton. In cestus, the epistomal, postoccipital, and subgenal sutures of the head a l l produce small internal ridges which make up part of the head endoskeleton, provide for muscle attachment, and undoubtedly add to the support of the exoskeleton. The ocular sclerite (Fig. 2 OSC), which frequently appears in general-ized insects as part of the exoskeleton surrounding the compound eyes and marked off from the rest of the cranium by an ocular suture, forms in A.  cestus an internal funnel-like flange, which separates the ommatidia of the compound eye from the rest of the organs of the head. Though this sclerite is part of the exoskeleton in generalized insects, i t definitely forms part of the endoskeleton of cestus. Except for a narrow margin around its basal part, this sclerite is almost completely black in colour. It is marked off from the rest of the cranium by an ocular suture (OS). The tentorium (Fig. 2, 4. 5. 6). The exoskeleton of insect heads is generally supported by an endo— skeletal framework, the evolution of which is s t i l l doubtful. This frame-work is referred to as the tentorium. In JU cestus, i t consists of a pair of anterior arms (Fig. 6 ATA), a pair of dorsal arms (DT), and a tentorial bridge (TB). The anterior tentorial arms are developed from invaginations of the epistomal ridge formed by the epistomal suture. Their formation causes a a pit-like impression on each side of the clypeus in the epistomal suture. The arms are narrow and rod-like. They are expanded mesally and laterally, producing broad transverse lamellae (TL), which probably give support to PLATE I Fig. 1. Dorsal aspect of head (25x). Fig. 2. Lateral aspect of head—compound eye removed to show ocular sclerite (25x). Fig. 3. Anterior aspect of head (25x). Fig. 4. Posterior aspect of head (2$x). Fig. 5. Posterior aspect of head—occiput and labio-maxillary complex removed to show endoskeleton (25x). Fig. 6. Anterior aspect of head—frons, vertex, and labio-maxillary complex removed to show endoskeleton (25x). AN—antennifer; ASG—antennal socket; AT—anterior tentorial pit; ATA— anterior tentorial arm; BS—basal antennal segment; CD—cardo; CLP--clypeus; DT--dorsal tentorial arm; E—compound eye; ES—epistomal suture; FR—frons; FOR—occipital foramen; GA—-galea; GEr—genae; HB—hypostomal bridge; ITRt— internal ridge; LB—labium; LBPLP^-labial palp; LIG—ligula; LM—labrumj LO—lateral ocellus; MD—mandible; MO—median ocellus; MXPLP--maxillary palp; OG)--occiput; OCC—occipital condyle; OCS—occipital suture; OS—ocular suture; OSC—ocular sclerite; PRTL—parietal; PT--posterior tentorial pit; SGE:—sub-gena; ST—stipes; TB>-tentorial bridge; TL~tentorial lamella; VX—vertex. 12. t h e g a n g l i o n a n d o t h e r o r g a n s o f t h e h e a d . T h e y e x t e n d p o s t e r o - d o r s a l l y t o t h e t e n t o r i a l b r i d g e . The v e n t r a l p a r t s o f t h e i r p o s t e r i o r h a l v e s a r e c o n t i n u o u s w i t h t h e h y p o s t o m a l b r i d g e ( H B ) , w h i c h i s s u p p o r t e d b y t h e m . The t e n t o r i a l b r i d g e i s a s e m i - r i n g - l i k e b a r b e t w e e n t h e p o s t e r i o r t e n t o r i a l p i t s ( F i g . 4, 5 P T ) , w h i c h a r e p i t - l i k e i m p r e s s i o n s v e n t r a l l y l o c a t e d o n e a c h s i d e o f t h e o c c i p i t a l f o r a m e n , p r o d u c e d b y i n v a g i n a t i o n s o f t h e e x o s k e l e t o n a t t h e s e p o i n t s t o f o r m t h e b r i d g e . I t i s homologous t o t h e p o s t e r i o r t e n t o r i a l a rms o f g e n e r a l i z e d i n s e c t s w h i c h , a c c o r d i n g t o S n o d g r a s s (1935), a r e " c o n t i n u o u s i n a t r a n s v e r s e b a r o r t e n t o r i a l b r i d g e , t h r o u g h t h e b a c k o f t h e h e a d " . The d o r s a l arms a r e s e c o n d a r y o u t g r o w t h s o f t h e a n t e r i o r a r m s . I n A . c e s t u s t h e y a r i s e j u s t a n t e r i o r t o t h e t e n t o r i a l b r i d g e a n d p a s s a n t e r o -d o r s a l l y t o t h e c r a n i a l w a l l where t h e y a r e s e c o n d a r i l y a t t a c h e d t o t h e p a r i e t a l s j u s t d o r s a d o f t h e a n t e n n a l s o c k e t s . The Head Appendages The t r o p h i . E x c e p t f o r some m o d i f i c a t i o n s i n t h e l a b i o - m a x i l l a r y c o m p l e x , t h e mouth p a r t s o f A ^ c e s t u s a r e v e r y g e n e r a l i z e d . T h e y a r e a d a p t e d f o r b i t i n g , r a s p i n g , a n d l a p p i n g . The l a b i u m ( F i g . 3, 6 LM) i s a m o d e r a t e l y l a r g e f l a p - l i k e p l a t e h i n g i n g o n t h e v e n t r a l m a r g i n o f t h e c l y p e u s . I t s e n t a l m a r g i n i s c o n t i n u -ous w i t h t h e membrane w h i c h f o r m s t h e r o o f o f t h e p r e o r a l c a v i t y . I n some i n s e c t s t h i s membrane b e a r s a s m a l l l o b e w h i c h hangs down i n t h e p r e -o r a l c a v i t y , t h e e p i p h a r y n x . I n JU c e s t u s t h i s membrane i s c u s h i o n - l i k e b u t does n o t f o r m a l o b e , a n d , t h e r e f o r e , c a n n o t r i g h t l y be c a l l e d a n e p i p h a r y n x . 13. The m a n d i b l e s ( F i g . 2, 3, 5, 6 MD; 1 3 A , 1 3 B , 13C) a r e t y p i c a l o f t h e b i t i n g j aws f o u n d i n t h e g e n e r a l i z e d g r o u p o f i n s e c t s . A t t h e b a s e t h e y a r e s u b t r i a n g u l a r i n shape w i t h t h e base o f t h e t r i a n g l e a r t i c u -l a t e d a t A a n d C o n t h e v e n t r a l m a r g i n o f t h e genae ( F i g . 2 A , G ) . D i s t a l l y t h e y a r e p o i n t e d , a n d b e a r o n t h e i r p o s t e r i o r m a r g i n s a s u b -a p i c a l t o o t h m a k i n g t h e m b i d e n t a t e . The l a b i o - m a x i l l a r y c o m p l e x ( F i g . 4 ) . I n g e n e r a l i z e d i n s e c t s t h e l a b i u m a n d m a x i l l a e a r e s e p a r a t e u n i t s , a n d a r e s e p a r a t e l y a t t a c h e d t o t h e m a r g i n o f t h e c r a n i u m , b u t i n J L c e s t u s , a s i n t h e m a j o r i t y o f Hymen-o p t e r a , t h e p o s t l a b i u m i s l a c k i n g , a n d t h e p r e l a b i u m i s s u s p e n d e d b y mem-b r a n e b e t w e e n t h e s t i p i t e s o f t h e two m a x i l l a e . T h i s c l o s e l y a s s o c i a t e s t h e l a b i u m w i t h t h e m a x i l l a r y appendages a n d t h e r e b y f o r m s a l a b i o - m a x i l l a r y c o m p l e x . When t h i s u n i t i s i n s i t u i t c o m p l e t e l y h i d e s t h e m a x i l l a r y c a r d i n e s f r o m v i e w . The m a x i l l a e ( F i g . 7, 8 , 9) p o s s e s s a l l t h e p a r t s t y p i c a l o f t h e p r i m i t i v e i n s e c t a m b u l a t o r y l i m b . The b a s e i s d i v i d e d i n t o a p r o x i m a l p a r t , t h e c a r d o ( C D ) , a n d a d i s t a l p a r t , t h e s t i p e s ( S T ) . The c a r d o a r t i c u l a t e s a t i t s b a s e w i t h a c o n d y l e o n t h e g n a t h a l m a r g i n o f t h e h y p o -s t o m a l b r i d g e , a n d d i s t a l l y w i t h t h e s t i p e s . The l a t t e r s c l e r i t e i s shaped i n s u c h a manner t h a t i t g i v e s t h e m a x i l l a a v e r y c l o s e a s s o c i a -t i o n w i t h t h e l a b i u m . L i k e t h e c a r d o , i t i s a t t a c h e d l a t e r a l l y t o t h e subgenae b y ample membrane. L a t e r a l l y , n e a r i t s t i p , t h e s t i p e s b e a r s a m o v a b l e f i v e - s e g m e n t e d p a l p ( M X P L P ) . I n g e n e r a l i z e d i n s e c t s t h e m a x i l -l a r y p a l p ha s a p a l p i f e r w h i c h i s p a r t o f t h e s t i p e s ; i n t h i s s p e c i e s t h e s t i p e s i s n o t d i f f e r e n t i a t e d i n t h i s m a n n e r . On i t s d i s t a l m a r g i n t h e s t i p e s b e a r s two m o v a b l e f l e s h y l o b e s : a n i n n e r l o b e , t h e l a c i n i a ( L C ) ; 1 4 . a n d a n o u t e r l o b e , t h e g a l e a ( G A ) . These a r e c l o s e l y a s s o c i a t e d w i t h t h e c o m p o s i t e l i g u l a ( L I G ) o f t h e l a b i u m when i n s i t u , a n d f o r m w i t h i t a b r u s h - l i k e r a s p i n g a n d l a p p i n g o r g a n . The l a b i u m ( F i g . 1 0 , 1 1 , 1 2 ) , a s s t a t e d a b o v e , c o n s i s t s o f a s i n g l e p a r t pre sumed b y t h e a u t h o r t o be t h e prementum (PMT) o f g e n e r a l i z e d i n s e c t s b e c a u s e i t b e a r s a l l t h e l a b i a l a p p e n d a g e s . N e a r i t s t i p , o n t h e l a t e r a l m a r g i n s , a r e t h e m o v a b l e f o u r - s e g m e n t e d l a b i a l p a l p s ( L B P I P ) . On i t s d i s t a l m a r g i n i s a l a r g e f l e s h y l o b e , t h e c o m p o s i t e l i g u l a ( L I G ) , f o r m e d b y f u s i o n o f t h e g l o s s a e o f g e n e r a l i z e d i n s e c t s . I t i s r e i n f o r c e d b y l i g h t l y - s c l e r o t i z e d r i d g e s w h i c h make i t a r a s p i n g o r g a n . I t s b a s e i s s t r e n g t h e n e d b y a p a i r o f s c l e r i t e s ( L S C ) . On e a c h s i d e o f t h e l i g u l a , i m m e d i a t e l y p o s t e r i o r t o t h e s e s c l e r i t e s , i s a f l e s h y l o b e . These a r e p r o b a b l y t h e p a r a g l o s s a e o f t h e more p r i m i t i v e i n s e c t s . The d o r s a l s u r f a c e o f t h e l i g u l a i s c o n t i n u o u s w i t h a h y p o p h a r y n g e a l l o b e , t h e h y p o p h a r y n x ( H P H ) , w h i c h , when i n s i t u , f o r m s w i t h t h e l i g u l a a s m a l l s a l i v a r y p o c k e t a t t h e b a s e o f w h i c h i s l o c a t e d t h e o p e n i n g o f t h e s a l i v a r y d u c t ( S L O ) . The a n t e n n a e . The a n t e n n a e i n A ^ c e s t u s ( F i g . 1 , 2, 3 B S ; 1 4 A , 1 4 B , 15) a r e t h r e a d -l i k e , many-segmented appendages on t h e f r o n t o f t h e h e a d . T h e y a v e r a g e 4 1 segments f o r e a c h s e x . The b a s a l segment (BS) i s l a r g e a n d b u l b o u s . I t a r t i c u l a t e s w i t h a c o n d y l e ( F i g . 1 , 3 AN) o n t h e l a t e r a l edge o f t h e a n t e n n a l s o c k e t ( A S O ) . The f o l l o w i n g segments a r e much s m a l l e r i n d i a -m e t e r , a n d a r e c y l i n d r i c a l i n s h a p e . The s e c o n d segment i s s m a l l e r t h a n t h e t h i r d w h i c h i s t h e longest segment o f a l l . The f o l l o w i n g segments become p r o g r e s s i v e l y s m a l l e r t o t h e t i p o f t h e a n t e n n a e , A s e n s o r y a p p a r a -t u s , J o h n s t o n ' s o r g a n , c o n s i d e r e d t o be p r e s e n t i n t h e s e c o n d segment o f PLATE II Fig, ?• Ental aspect of left maxilla (50x)« Fig, 8, Posterior aspect of left maxilla (50x), Fig, 9« Lateral aspect of left maxilla (50x). Fig, 10, Anterior aspect of labium (50x), Fig, U, Posterior aspect of labium (50x), Fig, 12, Lateral aspect of labium (50x). Fig, 13A, Anterior aspect of left mandible (50x)» Fig, 33F» Lateral aspect of left mandible (50x). Fig. 130, Fe-sterior aspect of left mandible (50x), Fig, 14A, Lateral aspect of the fourteenth segment of the female antenna (50x), Fig, 14B, Lateral aspect of the fourteenth segment of the male antenna (50x), Fig, 15, Cross-section of the twenty-second segment of the female antenna (50x), A—mandibular acetabulum; C—mandibular condyle; CD—cardo; GA—galea; HPH—hypopharynx; LBPLP—labial palp; LC—lacinia; LIG—ligula; LSC— ligular sclerite; MXPLP;—maxillary palp; PGL—paraglossa; PMT—prementum; SLO—opening of the salivary duct; SO—sensory organ; SP;—sensory pit; ST—stipes. 15. nearly a l l insect^ is not present in /L cestus. Each segment, except the first and second, bears a series of sensory pits (Fig. 14A, 1AB SP) which have no set pattern. These pits are much smaller and more plenti-ful in the segments of the male antennae. The eleventh to twenty-first segments (Fig, 14B) of the male antennae bear an ellipitical-shaped organ (SO), probably sensory in function; it is from five to thirty times larger than the sensory pits on the male antennae. None of these organs were found in the female antennae. The segments of the female antennae from the seventeenth to the end are flattened on the ventral side (Fig. 15). The sensory pits on this flattened surface are round and numerous. The Cervix The neck region of insects has been considered a separate body seg-ment by some writers, but studies by Crarapton (1917) showed this to be impossible. He pointed out that the neck region of insects is in every way homologous with the other intersegmental regions between the true thoracic segments and, therefore, cannot represent a true body segment. The fact that ganglia or other segmental structures are not found in this region of known insects in the embryonic or imaginal stages seems proof enough that this is really an intersegmental region. To deduce otherwise would mean acceptance of the intersegmental regions between the pro-, meso-, and metathoraces as body segments. In A± cestus the neck is almost completely hidden from view by the overlapping prothorax. However, when the head is pulled forward, the cervix shows as a short, narrow, membranous region containing, laterally, prong-like sclerites (Fig. 19, 21, 22, 23 V) which are fused with the episternum of the prothorax. These sclerites articulate anteriorly with 16. the occipital condyles of the head. This articulation limits the head to l i tt le , i f any, movement in the horizontal plane. The Thorax The thorax of most Hymenoptera is highly modified in comparison with the generalized insect thorax. In this respect i t is second only to the Diptera in the evolutionary scale of development. Many of the modifica-tions that have occurred in the thorax of the Hymenoptera are demonstrated by the thorax of A. cestus, such as: (1) the fusion of the first abdominal segment with the metathorax, and its incorporation into the thoracic divi-sion of the body; (2) the separation of the pronotum from the propectus, and its close association with the front of the mesothorax; (3) the concealment of the mesopostnotum and its phragma by invagination within the thoracic cavity; (4) the reduction of the pro- and metathoraces caused by the enlargment of the mesothorax to accomodate the concenbation of power in it for prope/llsion of the fore- and hind-wings; (5) the formation of a single, Large mesopleural plate on each side of the mesothorax by the narrowing of the mesepimeron, and the incomplete suppression of the meso-pleural suture; and (6) the formation of a prepectal plate in the meso-thorax, cut off from the anterior parts of both the mesosternum and meso-pleuron by the prepectal suture. The prothorax. In Aj_ cestus the prothorax is greatly reduced. The pronotum (Fig. 16, 17, 18, 19, 20 N^ ) is closely associated with the mesothorax. Dorsally it is a very narrow sclerite immediately anterior to the mesonotum (Fig. 25 N2); laterally i t broadens out and is extended towards the base of the wings. Its posterior ventral angles curve ventrally and almost meet. Its lateral prolongations practically make up the complete pleura of the PLATE: H I Fig. 16• Lateral aspect of thorax with head, abdomen, and thoracic appendages removed (17x). Fig. 17. Dorsal aspect of thorax with head, abdomen, and thoracic appendages removed (17x)» Fig. 18. Ventral aspect of thorax with head, abdomen, and thoracic appendages removed (17x). EPS]_—proepisternum; EPS2—mesoepisternum; NT_—pronotum; N3—metanotum; PL3—metapleuronj PPCT—prepectus; S]_—prosternum; —mesosternum; S3—metasternumj SCL2—mesoscutellumj SCT2—mesoscutumj TG—tegulaj V — c e r v i c a l sclerite; I T — f i r s t abdominal tergum, or;?prdpod_um. 17 anterior region of the thorax. The dorsal edge of the pronotum is slightly folded inwards forming a kind of resting seat for the ventral margin of the mesonotum. This fold partially encircles the first thora-cic spiracle (Fig. 19, 20 SP) which opens on the dorsal posterior comer of the pronotum. The propectus (Fig. 21, 22, 23) in Aj_ cestus is made up of the much reduced propleura (EPSj) and prosternum (S^ ) which together form a loose suspensorium for the prolegs. It is loosely attached to the pronotum by membrane. Each of the propleura consists of a single sclerite, the epi-sternum, which reaches forward in the neck region to the base of the head. Each proepisternal "plate is curved mesally over the ventral surface of the prothorax so that the two almost meet along the mid-line in front of the prosternum. In more generalized insects the propleura consist of two plates, an anterior proepisternum and a posterior proepimerony which are divided by a pleural suture. No such suture was located on the propleuron of A., cestus, and, therefore, it is assumed that the two sclerites have fused together solidly or that the proepimeron has been completely lost. A horizontal ridge divides the propleura into an upper and lower region, but this is not the pleural suture found in the more generalized forms. Anteriorly the propleura overlaps the neck region. Internally, at this region, they each present a shelf-like horizontal apodeme (Fig. 21 V), inflected from submarginal grooves on their outer surface. Distally these apodemes expand anteriorly and posteriorly in such a manner that they give, anteriorly, excellent articulatory surfaces for the occipital condyles of the head, and, posteriorly, an apodeme for attachment of pro-thoracic muscles. This has evolved, according to Snodgrass (1935), from P L A T E I V F i g . 19* L a t e r a l a s p e c t o f p r o t h o r a x (25x). F i g . 20. D o r s a l a s p e c t o f p r o n o t u m (25x). F i g . 21. D o r s a l a s p e c t o f t h e p r o p e c t u s s h o w i n g t h e p r o t h o r a c i c e n d o s t e m u m , a n d a r t i c u l a t i o n o f p r o p e c t u s w i t h t h e h e a d (25x). F i g . 22. V e n t r a l a s p e c t o f t h e p r o p e c t u s (25x). F i g . 2 3 . L a t e r a l a s p e c t o f t h e p r o p e c t u s (25x). F i g . 24« D o r s a l a s p e c t o f t h e m e s o p e c t u s w i t h meso-notum removed t o show t h e m e s o t h o r a c i c e n d o s t e r n u m (25x). A — p l e u r a l a p o p h y s i s ; A ] _ — a n t e r i o r a p o p h y s i s o f t h e m e s o e n d o s t e r n u m ; B — p o s t e r i o r a p o p h y s i s o f c e r v i c a l s c l e r i t e ; B S — b a s i s t e r n u m ; G — a n t e r i o r a r m o f e n d o s t e m u m ; C X ^ — p r o t h o r a c i c c o x a ; D — l a t e r a l a r m o f e n d o s t e r n u m ; D A — d o r s a l a p o p h y s i s ; E P S ^ — p r o e p i s t e r n u m ; EPS2—mesoepisternum; F S — f u r c a . s t e r n u m ; F U — f u r c a o r e n d o s t e m u m ; — p r o n o t u m ; O C C — o c c i p i t a l c o n d y l e ; P P G T — p r e p e c t u s ; P R — p l e u r a l r i d g e ; S- j_—prosternum; S2—mesosternum; S P — t h o r a c i c s p i r a c l e ; V — c e r v i c a l s c l e r i t e ; ¥ — l a t e r a l e x t e n s i o n o f f u r c a ; W P — p l e u r a l w i n g p r o c e s s . 2 4 18 a f u s i o n o f t h e n e c k s c l e r i t e s f o u n d i n more p r i m i t i v e i n s e c t s t o t h e p r o p l e u r a . I n S n o d g r a s s (1942) i t i s named t h e c e r v i c a l apodeme. The p r o s t e r n u m i s a s m a l l , t r i a n g u l a r - s h a p e d s c l e r i t e l y i n g b e t w e e n t h e f r o n t coxae ( C X 3 . ) a n d b e h i n d t h e v e n t r a l p a r t s o f t h e e p i s t e r n a . I n A . c e s t u s ( F i g . 2 1 , 2 2 , 2 3 ) i t c o n s i s t s o f a n a n t e r i o r , t r i a n g u l a r - s h a p e d s c l e r i t e , t h e b a s i s t e r n u m ( B S ) , a n d a p o s t e r i o r , o v a l - s h a p e d s c l e r i t e , t h e f u r c a s t e r n u m ( F S ) . The l a t t e r i s f o l d e d d o r s a l l y so t h a t i t f o r m s a r i g h t - a n g l e w i t h t h e b a s i s t e r n u m . I t i s f r o m t h i s s c l e r i t e t h a t t h e e l a b o r a t e e n d o s k e l e t o n o f t h e p r o t h o r a x i s d e v e l o p e d . T h e s e s c l e r i t e s a r e b l a c k i n c o l o u r . The p r o t h o r a c i c e n d o s k e l e t o n ( F i g . 2 0 , 2 1 , 2 3 ) i n A j , c e s t u s c o n -s i s t s m a i n l y o f f o u r p a r t s : a p a i r o f d o r s a l p h r a g m a s , two p a i r s o f p l e u r a l apodemes , a n d a s t e r n a l a p o p h y s i s . The l a t t e r i s much l a r g e r t h a n t h e o t h e r s a n d o c c u p i e s much o f t h e i n t e r i o r o f t h e p r o p e c t u s . The d o r s a l phragmas ( F i g . 2 0 DA) g i v e a t t a c h m e n t f o r t e r g o p l e u r a l m u s c l e s w h i c h a r e i n s e r t e d on t h e p o s t e r i o r p l e u r a l a p o p h y s e s ( F i g . 2 1 A ) . The c e r v i c a l s c l e r i t e s (V) a r e s l i g h t l y p r o d u c e d p o s t e r i o r l y , a n d f o r m a s e c o n d p a i r o f p l e u r a l apodemes (B) f o r f u r t h e r m u s c l e a t t a c h m e n t . The s t e r n a l a p o p h y s i s i s much more c o m p l i c a t e d t h a n t h e a b o v e e n d o s k e l e t a l p a r t s . I t i n c l u d e s a p a i r o f l a t e r a l l y d i v e r g e n t w i n g s , o r f u r c a e , w h i c h e x t e n d t o t h e d o r s a l edge o f t h e p r o p l e u r o n t o w h i c h t h e y a r e u n i t e d i m m e d i a t e l y a n t e r i o r t o t h e p o s t e r i o r p l e u r a l apodemes ( A ) . These w i n g s f o r m a b r i d g e (D) o v e r t h e c o x a l c a v i t y . T h e y a r e e x t e n d e d a n t e r -i o r l y p r o d u c i n g a n o t h e r p a i r o f a p o p h y s e s ( C ) . The p t e r o t h o r a x . T h i s i s t h e w i n g - b e a r i n g s e c t i o n o f t h e t r u n k , a n d i n A . c e s t u s 19. i s made up of three body segments: the mesothorax, the metathorax, and the f i r s t abdominal segment of other i n s e c t s . These three segments are inti m a t e l y united to form a mechanical u n i t supporting the wings, the middle and hind l e g s , and the abdomen. Between the t h i r d pterothoracic segment, or propodeum, and the abdomen, there i s a deep c o n s t r i c t i o n which i s t y p i c a l of the sub-order C l i s t o g a s t r a to which t h i s species belongs. The dorsum of the pterothorax i s e a s i l y d i f f e r e n t i a t e d i n t o i t s component parts. These are: a large a n t e r i o r p l a t e , the mesonotum ( F i g . 25 N2); a small, narrow pl a t e , the metanotum (F i g . 29 M^); and a broad, quadrangular p l a t e , the propodeum, or true f i r s t abdominal tergum ( F i g . 28 I T ) . The l a t t e r i s s o l i d l y anchylosed with the metapleural s c l e r i t e s . Unlike the dorsal surface, the s t e r n a l surface of the pterothorax i s made up of two pl a t e s : a large a n t e r i o r p l a t e , the mesosternum ( F i g . 27 S2); and a smaller p o s t e r i o r p l a t e , the metasternum ( F i g . 30 S3). These are completely fused with the pleura of t h e i r respective segments. They are separated from each other by a suture between the coxae of the middle l e g s . The sternum of the f i r s t abdominal segment has been l o s t i n t h i s species. The pleura of the pterothorax c o n s i s t s of two p a i r s of s c l e r i t e s : a large a n t e r i o r p a i r , the mesopleura ( F i g . 25 EPS2); and a smaller poster-i o r p a i r , the metapleura ( F i g . 28 PL3). Both p a i r s are continuous with the sternum of t h e i r respective segments. The l a t t e r p a i r are a l s o con-tinuous with the f i r s t abdominal tergum. This p a i r , though continuous with the f i r s t abdominal tergum and the metasternum, are d i f f e r e n t i a t e d from them by prominant ri d g e s . 20. The m e s o t h o r a x . T h i s i s t h e p o w e r - h o u s e o f JL c e s t u s . I t i s t h e l a r g e s t b o d y s e g -m e n t , a n d i t s s c l e r o t i c s u r f a c e s a r e c o r r e s p o n d i n g l y l a r g e . The n e e d f o r s t r e n g t h t o h o l d t h e i n c r e a s e d power h a s n e c e s s i t a t e d c l o s e a s s o c i a t i o n o f t h e a d j o i n i n g segments a n d f u s i o n o f t h e c l o s e l y - r e l a t e d s c l e r i t e s p r e s e n -t e d b y t h e m e s o t h o r a x o f g e n e r a l i z e d i n s e c t s . The mesonotum ( F i g . 25 N2) e x t e r n a l l y c o v e r s a l i t t l e more t h a n t h e a n t e r i o r - h a l f o f t h e t h o r a c i c d o r s a l s u r f a c e . T h i s p a r t i s d i v i d e d i n t o t w o a r e a s : t h e mesoscutum (SCT2), a n d t h e m e s o s c u t e l l u m (SCL2). The d i v i s i o n a l f i s s u r e (TS) i s i m m e d i a t e l y b e h i n d a b r o a d , deep f u r r o w o n t h e The l a t e r a l m a r g i n s o f t h e s c u t u m a n d t h e s c u t e l l u m a r e a b r u p t l y c u r v e d v e n t r a l l y . p o s t e r i o r m a r g i n o f t h e s c u t u m . / T h e y p r e s e n t l a t e r a l s u r f a c e s w h i c h , i n t h e c a s e o f t h e s c u t u m , f o r m , p o s t e r i o r l y , t h e n o t a l w i n g p r o c e s s e s (ANP) a n d (PNP) f o r t h e n o t a l a r t i c u l a t i o n o f t h e f i r s t a n d t h i r d a x i l l a r y s c l e r i t e s o f t h e f i r s t p a i r o f w i n g s . A n t e r i o r l y i t f o r m s t h e p r e p h r a g m a (APH2) a n d a n a r r o w , a n t e r i o r , l a t e r a l s u r f a c e w h i c h i s c l o s e l y a s s o c i a t e d w i t h t h e d o r s a l i n f l e c t i o n o f t h e p r o n o t u m when i n s i t u . The l a t e r a l s u r -f a c e s o f t h e s c u t e l l u m e x t e n d a n t e r i o r l y a s h o r t d i s t a n c e b e y o n d t h e p o s t -b e r i o r e x t r e m i t y o f t h e s c u t u m w h e r e t h e y p r o a d e n o u t l a t e r a l l y a n d f o r m s m a l l h o o d s w h i c h p a r t i a l l y c o v e r t h e b a s i s o f t h e h i n d - w i n g s ( F i g . 26). These a p p e a r t o b e t h e homologues o f t h e i n n e r squamae f o u n d i n t h e t h o r a x o f D i p t e r a . These l a t e r a l s u r f a c e s a r e d i f f e r e n t i a t e d f r o m t h e d o r s a l s u r f a c e o f t h e s c u t e l l u m a n d t h e p o s t e r i o r p a r t o f t h e s c u t u m b y a r i d g e w h i c h e x t e n d s t o n e a r t h e p o s t e r i o r m a r g i n o f t h e s c u t e l l u m . The f u r r o w a l o n g t h e p o s t e r i o r m a r g i n o f t h e s c u t u m i s a b r u p t l y t e r m i n a t e d a t i t s ends b y t h e s e r i d g e s . 21. The m e s o p o s t n o t u m ( F i g . 25, 26 PN2) i s a s e m i - s c l e r o t i c s u r f a c e a t t a c h e d t o t h e p o s t e r i o r m a r g i n o f t h e s c u t e l l u m . I t i s c o n t i n u o u s w i t h a v e r y l a r g e p o s t p h r a g m a (PPH2) w h i c h e x t e n d s f a r i n t o t h e m e t a t h o r a c i c c a v i t y . The l a t e r a l e x t r e m i t i e s o f t h e p o s t n o t u m a r e c o n t i n u o u s w i t h t h e d o r s a l p o s t e r i o r c o r n e r s o f t h e m e s e p i m e r a (EPLl j ) o f t h e m e s o p l e u r a . The p o s t n o t u m a n d t h e p o s t e r i o r phragma a r e c o m p l e t e l y i n v a g i n a t e d i n t o t h e m e t a -t h o r a c i c c a v i t y , a n d a r e v i s i b l e o n l y when t h e m e t a t h o r a c i c segment i s removed f r o m t h e m e s o t h o r a x . The m e s o p l e u r a ( F i g . 16, 17, 1 8 , 25, 26, 27 E P S 2 , E P M 2 ) a r e t h e l a r g e l a t e r a l p l a t e s o f t h e m e s o t h o r a x c o n t i n u o u s v e n t r a l l y w i t h t h e s t e r n u m ( F i g . 27 82). E a c h p l e u r o n i s d i v i d e d b y a s c u l p t u r e d p l e u r a l s u t u r e ( F i g . 25 PS) i n t o a l a r g e a n t e r i o r s c l e r i t e , t h e e p i s t e r n u m (EPS2), w h i c h p r a c t i c a l l y makes u p t h e w h o l e o f t h e p l e u r o n , a n d a n a r r o w p o s t e r i o r s c l e r i t e , t h e e p i m e r o n (EPM2). The a n t e r o - d o r s a l m a r g i n o f t h e f o r m e r i s p r o d u c e d d o r s a l l y , f o r m i n g a b r o a d p l e u r a l w i n g p r o c e s s (WP) w h i c h a c t s a s a f u l c r u m f o r t h e f r o n t - w i n g . The p r e p e c t u s ( F i g . 16, 1 8 , 24, 25, 27 PPGT ) i s t h e b r o a d p l a t e be tween t h e m e s o s t e r n u m ( F i g . 16 S2)* m e s e p i s t e r n a (EPS2), a n d t h e p r o -notum ( N j ) . T h i s p l a t e i s a p u r e l y s e c o n d a r y p r o d u c t i o n i n t h e Hymenop-t e r a ( S n o d g r a s s 1911). I t i s d i v i d e d f r o m t h e f o r m e r a r e a s b y a s c l e r o t i c r i d g e . The m e s o s t e r n u m ( F i g . 16, 1 8 , 24, 25, 27 S2) i s t h e s c l e r o t i c r e g i o n f o r m i n g t h e b r o a d u n d e r s u r f a c e o f t h e m e s o t h o r a x . P o s t e r i o r l y i t i s c u r v e d d o r s a l l y a n d f o r m s a s m a l l s c l e r o t i c r e g i o n b e t w e e n t h e c o x a e o f coith t h e m i d d l e l e g s w h i c h a r e synonymous t e - t h e f u r c a s t e r n u m o f t h e p r o t h o r a x ( F i g . 24). The s t e r n u m a n d p r e p e c t u s a r e d i v i d e d a l o n g t h e i r m e d i a n l i n e PLATE V Fig. 25. Lateral a s p e c t o f m e s o t h o r a x — a p p e n d a g e s r e m o v e d (25x). Fig. 26. Dorsal a s p e c t o f m e s o t h o r a x - t - a p p e n d a g e s , r e m o v e d (25x). Fig. 27. Ventral a s p e c t of m e s o t h o r a E X — a p p e n d a g e s r e m o v e d (25x)« A N F ! — a n t e r i o r n o t a l w i n g p r o c e s s ; A P H 2 — m e s o t h o r a e i c p r e p h r a g m a ; E P M 2 ~ m e s o e p i m e r o n ; E P S 2 — m e s o e p i s t e r n u m ; N 2 — m e s o n o t u m ; P K 2 — m e s o t h o r a -c i c p o s t n o t u m ; P N P — p o s t e r i o r n o t a l w i n g p r o c e s s ; P P C T — m e s o t h o r a e i c p r e p e c t u s ; P P H 2 — m e s o t h o r a e i c p o s t p h r a g m a ; P S — p l e u r a l s u t u r e ; S 2 — m e s o -s t e r n u m ; S G I g — m e s o s c u t e l l u m ; ' S G T 2 — m e s o s c u t u m ; T G — t e g u l a ; T S — t r a n s v e r s e s u t u r e ; W P — p l e u r a l w i n g p r o c e s s . 22. by a deep suture which marks the point of invagination of adjoining sclerites to form the large endostemum of the mesothorax. The endoskeleton of the mesothorax (Fig. 24, 25, 26, 27). In A. cestus the internal ridges formed by the transverse fissure (Fig. 26 TS), the pleural suture (Fig. 25 PS), the prephragma (Fig. 25, 27 A P H 2 ) , the postphragma (Fig. 25 , 26, 27 P P H 2 ) , and the endostemum (Fig. 24 FU) make up the endoskeleton of the mesothorax. The endostemum extends from the prepectus to the posterior part of the mesosternum. Immediately posterior to its middle part it is produced laterally into wing-like structures (Fig. 24 W) which extend to the pleura where they are attached in front of the pleural ridge (PR). The wings coalesce dorsally and extend anterior-ly into an anterior median apophysis {Aj), Between the dorsal coalescence and the base an oval-shaped aperture is formed through which passes the ventral nerve cord. The ventral terminations of the pleural ridges extend into the coxal cavities and form articulatory condyles for the coxae of the mesothoracic legs. The metathorax (Fig. 16. 17. 18, 28, 29. 30)., In Aj_ cestus the metathorax, like the prothorax, is much reduced in size. Its apparent functions are to present articulatory surfaces for the hind-wings and hind legs, and to house the muscles used to move the latter. Its pleura are fused dorsally with the notum of the first CLboCominaJ thoraeio segment which contains the second pair of thoracic spiracles (true first abdominal spiracles), and forms a cap over the posterior part of the thoraxe The metanotum (Fig. 28, 29 N3) is a very narrow, sculptured sclerite between the mesoscutellum and the propodeum. It bears on its lateral 23. extremities the anterior and posterior notal wing processes of the hind-wings. The metapleuron (Fig. 28, 29, 30 PL-) is extensively modified and its sclerites show little homology with those of the generalized insect wing-bearing thorax. It is fused with both the metasternum (Fig. 30 S3) and the propodeum (IT), forming with them a complete unit which composes the posterior third of the thorax. Each pleuron is separated into a small anterior triangular portion and a larger posterior part by a sculptured furrow which crosses the anterior margin of the propodeum and terminates at the lateral extremities of the metasternum. The anterior portion is extended dorsally to the metanotum (Fig. 29 N3). It bears the metapleural wing process (WP) which acts as a fulcrum for the hind-wings. The post-erior part of the metapleuron bears a small condyle which extends into the coxal cavity of the hind leg for its articulation with the segment. The metasternum (Fig. 16, 18, 28, 30 S3) is the large ventral plate of the metathorax. It is slightly concave anteriorly on each side of the mid-line to accomodate the large coxae of the hind legs. It extends to - the posterior aperture of the thorax in which is inserted the abdominal petiole, or constricted second abdominal segment. The propodeum (Fig. 16, 17, 28, 29 IT) is a large, heavily-sculptured, convex plate covering the posterior part of the pterothorax. Laterally it contains the spiracles (Fig. 28, 29 ISP) of its segment. Posteriorly with it descends steeply to the abdominal petiole which articulates oa two internal condyles presented by the former. On each side, at the top of the descending slope, the propodeum is extended into prominent blunt spines. Though this plate is commonly termed the propodeum, i t is really PLATE V/I F i g i 2 8 . L a t e r a l a s p e c t o f m e t a t h o r a x — a p p e n d a g e s removed (25x). F i g . 2 9 . D o r s a l a s p e c t o f m e t a t h o r a x — a p p e n d a g e s removed (25x). F i g . 30. V e n t r a l a s p e c t o f m e t a t h o r a x — a p p e n d a g e s removed (25x). F U — m e t a e n d o s t e r n u m ; — m e t a n o t u m ; P L - — m e t a p l e u r o n j — m e t a s t e r n u m ; W P ^ - p l e u r a l w i n g p r o c e s s ; I S P * - - f i r s t a b d o m i n a l s p i r a c l e ; I T — f i r s t a b d o m i n a l t e r g u m , o r p r o p o d e u m . I WP WP 24. the propodeal tergum. In the honey bee (Snodgrass 1942), the propodeal sternum is represented by a narow ventral plate behind the bases of the hind legs, but in A. cestus the propodeal sternum appears to be lost or completely fused with the metasternal plate. The propodeal tergum of many Clistogastra is divided into various areas which present sound morphological characteristics for species des-criptions. These areas are obscured by sculpturing in Aj_ cestus, and are therefore insignificant in this species. The metathoracic endoskeleton (Fig. 30 FU) mainly consists of a pair of arch-like endosternal arms. They are broadened in the middle, and attached laterally to a strong ridge which is produced by the sculptured external furrow. This furrow differentiates the propodeum and posterior part of the metapleura from the metanotum and anterior part of the meta-pleura. The Legs The legs of cestus are of the cursorial type. The metathoracic legs are considerably larger than the prothoracic and mesothoraeic pair. The insect probably uses these legs to jump into the air prior to flight. Each leg (Fig. 34 to 36) is made up of a basal segment, the coxa (Cx^, Cx£, CXj), a trochanter (TR), a femur (FM), a tibia (TB), and a tarsus (TAR). Therefore, except for the basal subdivision of the femur (FM]_), the legs of Aj_ cestus are very similar to those found in generalized insects. The tibiae of the prothoracic legs bear, distally, a large movable spur, or calcar (Fig. 34 CC). There are two such movable spurs on each tibia of the meso- and metathoracic legs (Fig. 35, 36 CO). The tarsus of each leg is five-segmented. The fi r s t segment in each case is much larger than the following ones. On the end of the f i f t h PLATE VII Fig, 31, Ventral aspect of metathoracic pretarsus (50x), Fig, 32, Dorsal aspect of metathoracic pretarsus (5Qx), Fig, 33, Lateral aspect of metathoracic pretarsus (50x), Fig, 34, Anterior aspect of prothoracic leg (15-0. Fig, 35, Anterior aspect of mesothoracic leg (15x), Fig, 36, Anterior aspect of metathoracic leg (15x), AR—arolium; CA—camera; CO:—calcar; GX^—prothoracic coxa1; CX2—meso- -thoracic coxa; CX-j—metathoracic coxa; FM—femur; FM]_—basal segment of femur; OR—orbicula; TAR—tarsus; TB—tibia; TR—trochanter; UN—ungues; UNG—unguitractor. 25. segment there are a number of sclerites, collectively termed the pretarsus. The pretarsus is similar in a l l six legs, and differs very l i t t l e , i f any, from that of the generalized insect. It consists, essentially, of a pair of large lateral claws, the ungues (Fig. 31, 32, 33 UN), and a median fleshy lobe, the arolium (AR). The ungues are curved ventrally at their ends and are pointed. They articulate dorsally with the last tarsal segment, or last tarsomere. The arolium is supported dorsally by a flask-shaped sclerite, the oricula (Fig. 32, 33 OR), and ventrally by a rectangular sclerite, the calcanea, or unguitractor (Fig. 31/33 UNG). Distally i t is supported by an incomplete ring-like sclerite, the camera (Fig. 31 to 33 CA). The terminology for the pretarsus was taken from Bucher (1948). The leg articulations. The leg articulations are very similar to those of generalized insects. Each coxa (Fig. 37 Cxp 38 0x2, 39 Cx^) is articulated primar-i l y with a pleural condyle which extends into the coxal cavity. In generalized insects, this condyle is usually an extension of the pleural ridge formed by the pleural suture; however, in cestus the relation of the pleural-coxal condyle to the lower end of the pleural ridge is obscured in the pro- and metathoraces due to the modification of the pleural scler-ites in these segments. The meso- and metathoracic coxae are closely associated with the sterna of their respective segments, and their move-ments are almost completely restricted to an oblique transverse plane. This is a secondary association which is a specialization occurring in the higher insects (Snodgrass 1935). The procoxae, on the other hand, are very loosely associated with the sterna of the prothorax, and their move-ments are not by any means as restricted as are those of the meso- and PLATE VIII Fig. 37. Dorsal aspect of coxopleural articulation of the prothoracic leg (50x). Fig. 38. Dorsal aspect of coxopleural articulation of the mesothoraeic leg (50x). Fig. 39. Dorsal aspect of coxopleural articulation of the metathoracic leg (50x). Fig. 40. Coxotrochanteral articulation of the left prothoracic leg (50x). Fig. 41. Coxotrochanteral articulation of the left mesothoraeic leg (50x). Fig. 42. Coxotrochanteral articulation of the left metathoracic leg (50x). Fig. 43. Trochantero-femural articulation of the left prothoracic leg (50x). Fig. 44. Trochantero-femural articulation of the left mesothoraeic leg (50x). Fig. 45. Trochantero-femural articulation of the left metathoracic leg (50x). Fig. 46. Tibio-femural articulation of the left prothoracic leg (50x). Fig. 47. Tibio-femural articulation of the left mesothoraeic leg (5Qx). Fig. 48. Tibio-femural articulation of the left metathoracic leg (50x). Fig. 49. Tibio-tarsal articulation of the left prothoracic leg (50x)« Fig. 50. Tibio-tarsal articulation of the left mesothoraeic leg (50x), Fig. 51. Tibio-tarsal articulation of the left metathoracic leg (50x). CX]_—prothoracic coxa; CX2—mesothoraeic coxa; CX3—metathoracic coxa; EPSi—proepisternum; EPS2—mesoepisternum; EPS3—metaepisternum; FM—femur; FM^—basal segmentation of the femur; TAR—tarsus; TB—tibia; TR—trochanter; J3l—posternum; S2—mesosternum; Sj—metasternum. 26. metathoracic coxae. The coxotrochanteral articulation of each leg is dicondyiic (Fig. 40, 41, 42), and the movements at this joint are restricted to a perpendicular plane. The trochantero-femoral joint (Fig. 43, 44, 45) of each leg is without any condylar articulation, and, though pliable in a l l directions, its movements are very restricted. The joints of the femur and tibia, and those of the tibia and tarsus are dicondyiic in each leg (Fig. 46, 47, 48, 49, 50, 51). The Wings In insects the wing veins and the cells formed by them often present morphological characteristics which are of considerable importance in the identification of species. In the past much work has been done on the wings and their veins. One of the more important contributions made was that of Comstock and Needham (1898-1899). Adopting the terminology of Redtenbacher, they developed a venational nomenclature that is s t i l l widely used for naming the veins of most insect wings. At the same time, they devised a hypothetical wing from studies of wing tracheae which precede and, in a general sense, determine the courses of the veins. This was to represent the primitive insect wing. Since them considerable contention has arisen concerning the correctness of the Comstock-Needham interpretation of the primitive wing. From Imms (1937) we note that Tillyard questioned the Comstock-Needham interpretation of the cubital vein, and from ontogenetical studies he concluded that this vein originally had three branches instead of two as was concluded by the former authors. Snodgrass (1935) from studies of wing veins and their associations with the axillary sclerites concluded that the Comstock-Needham first anal vein was really the post cubitus. Furthermore, we note that studies of Lamere in 1922 upheld the views of 27. R e d t e n b a c h e r c o n c e r n i n g t h e f a c t t h a t t h e m a i n v e i n s o f i n s e c t w i n g s p r i m i -t i v e l y a l t e r n a t e d a s c o n v e x a n d c o n c a v e v e i n s , a d e d u c t i o n f o r m e r l y d i s m i s s e d b y C o m s t o c k a n d Needham. The w i n g s o f t h e H y m e n o p t e r a a r e h i g h l y m o d i f i e d i n c o m p a r i s o n w i t h t h o s e o f g e n e r a l i z e d i n s e c t s . The f i r s t a t t e m p t s made t o h o m o l o g i z e t h e w i n g v e i n s o f t h i s o r d e r w i t h t h o s e o f more p r i m i t i v e a n d g e n e r a l i z e d o r d e r s were t h o s e o f M a c G i l l i v r a y (1906) a n d C o m s t o c k (1917). T h e i r u s e o f t h e Comstock-Needham s y s t e m r e s u l t e d i n a r t i f i c i a l a n a l o g i e s w h i c h w e r e c u m b e r -some a n d u n s a t i s f a c t o r y f o r u s e b y h y m e n o p t e r a n s y s t e m a t i s t s , A more a p p l i -c a b l e n o m e n c l a t u r e was d e v e l o p e d b y Rohwer a n d Gahan (1916), b u t i t , t o o , i s a r t i f i c i a l , a n d t h o u g h w i d e l y u s e d does n o t h e l p p r e s e n t s y s t e m a t i s t s t o c o n s t r u c t n a t u r a l k e y s f o r p r o p e r c l a s s i f i c a t i o n o f t h e H y m e n o p t e r a , F o r b e s (1925) a t t e m p t e d t o c o r r e l a t e t h e d e v e l o p m e n t o f t h e h y m e n o p t e r a n w i n g v e i n s w i t h t h o s e o f t h e C o l e o p t e r a , b u t h i s c o n c l u s i o n s , l i k e t h o s e o f C o m s t o c k and Needham, a r e b a s e d o n t h e s t u d i e s o f w i n g t r a c h e a e , a n d a r e c o n s i d e r e d p r o b l e m a t i c . A r e c e n t s t u d y o n t h e h o m o l o g i e s o f t h e w i n g v e i n s o f t h e s a w f l i e s ( T e n t h r e d i n i d a e ) b y R o s s (1936) ha s r e s u l t e d i n a g e n e r a l a c c e p t a n c e o f l o n g - k n o w n p r i n c i p l e s , R o s s b a s e d h i s s t u d i e s o n : (1) t h e s i g n i f i c a n c e o f t h e c o n v e x - c o n c a v e a l t e r n a t i o n o f t h e m a i n v e i n s i n t h e p r i m i t i v e i n s e c t w i n g , a p r i n c i p l e a d v o c a t e d b y R e d t e n b a c h e r i n 1886; a n d (2) t h e a s s o c i a -t i o n o f t h e m a i n w i n g v e i n s w i t h t h e a x i l l a r y s c l e r i t e s o f t h e w i n g s , a p r i n c i p l e a d v o c a t e d b y S n o d g r a s s (1935), Thus he was a b l e t o show d i s t i n c t a f f i n i t i e s be tween t h e w i n g s a n d v e i n s o f t h e Hymenoptera a n d t h o s e o f t h e M e c o p t e r o i d a n d P a n o r p d d o r d e r s , e s p e c i a l l y t h e M e g a l o p t e r a , M e c o p t e r a , a n d T r i c h o p t e r a . The a s s o c i a t i o n o f t h e H y m e n o p t e r a w i t h t h e s e o r d e r s was b a s e d on t h e P a n o r p o i d Complex o f T i l l y a r d . U s i n g t h e s e p r i n c i p l e s , 28. Ross c o n s t r u c t e d a new h y p o t h e t i c a l w i n g w i t h w h i c h t h e wings and v e i n s o f t h e modern Hymenoptera c a n e a s i l y be h o m o l o g i z e d . T h i s new i n t e r p r e t a t i o n o f t h e p r i m i t i v e - t y p e h y m e n o p t e r a n wing i s g a i n i n g more a n d more r e c o g n i -t i o n i n t h e f i e l d o f s y s t e m a t i c s . The v e n a t i o n a l n o m e n c l a t u r e d e v e l o p e d b y R o s s ha s r e c e n t l y b e e n u s e d b y Riegel (1948) i n h i s i n t e r p r e t a t i o n o f t h e w i n g v e i n s o f c e r t a i n h y m e n o p t e r a n i n s e c t s b e l o n g i n g t o t h e B r a c o n i d a e f a m i l y . The p r e s e n t a u t h o r , l i k e R i e g e l , h a s a d o p t e d R o s s ' s n o m e n c l a t u r e i n h i s i n t e r p r e t a t i o n o f t h e w i n g v e i n s o f c e s t u s . The f o r e - w i n g ( F i g . 52A). I n o r d e r t o h o m o l o g i z e t h e w i n g v e i n s o f A^ c e s t u s w i t h t h o s e o f t h e h y p o t h e t i c a l w i n g d e v e l o p e d b y R o s s , we must assume t h a t c o n s i d e r a b l e m i g r a t i o n a n d s u b s e q u e n t f u s i n g o f v e i n s ha s o c c u r r e d . I n t h e f r o n t w i n g t h e c r o s s - v e i n s have been so a r r a n g e d t h a t t h e y a d e q u a t e l y c o u n t e r a c t t h e b a c k w a r d f o r c e p l a c e d on t h e m b y t h e a t t a c h m e n t o f t h e h i n d - w i n g t o them b y t h e h a m u l i . The r a d i u s ha s m i g r a t e d a n t e r i o r l y a n d f u s e d w i t h t h e c o s t a , f o r m i n g a s t r o n g , b r o a d m a r g i n a l v e i n (C + R ) . The s u b c o s t a l v e i n h a s b e e n g r e a t l y r e d u c e d , a n d i s r e p r e s e n t e d b y t h e l a r g e b a s a l s c a l e ( F i g . 53 t o 56 SC) and t h e s t i g m a ( F i g . 52A S T ) . The f i r s t c u b i t a l v e i n ha s f u s e d w i t h t h e base o f t h e m e d i a and has p r o d u c e d a h e a v y m e d i a n v e i n (M • Cu^) w h i c h i s c o n t i n u o u s a t i t s b a s e w i t h t h e r a d i u s . The a n a l v e i n s have b e e n r e d u c e d t o t w o (1A, 2A). The b r a n c h e s o f t h e r a d i u s h a v e b e e n r e d u c e d t o t w o : r a d i u s one (R]_), a n d t h e r a d i a l s e c t o r ( R S ) . The b r a n c h e s o f t h e m e d i a a r e a l l f u s e d i n t o one v e i n ( M ) . The m i d d l e p a r t o f t h i s v e i n h a s m i g r a t e d a n t e r i o r l y i n s u c h a way t h a t i t u n i t e s w i t h t h e s t r o n g m a r g i n a l v e i n (C + R) a n d p r o d u c e s a l o n g c r o s s - v e i n b e t w e e n i t a n d t h e m e d i a n v e i n (M + Ouj), The d i s t a l p a r t o f t h e m e d i a c o n t i n u e s t o t h e d i s t a l m a r g i n o f o f t h e w i n g . I t i s c o n n e c t e d t o t h e r a d i a l s e c t o r b y t w o c r o s s - v e i n s 29, (1R-M) and (2R-M) which enclose a small ce l l characteristic of the Ichneu-monid fore-wing. The cubital vein is represented by its anterior branch only (Cu^), the base of which forms with the base of the media (M) the heavy median vein (H t Cu ). After branching from this vein, i t is branched into two subsidiary branches (Cu-ja) and (Cu^b). The former continues to the distal margin of the wing. It is parallel to the distal part of the median vein (M), and is connected to i t by the cross-vein (2M-Cu). The second branch (Cu^b) forms a cross-vein between the distal end of the first anal vein and Cu^. Cu^ is united to the distal part of the median vein by the cross-vein (lM-Cu). A second cross-vein (Cu-A), between Cu-^  and the first anal (1A), is almost continuous with the middle part of the median vein, and the two form a long cross-vein between the marginal vein (C * R) and the first anal vein (1A). This undoubtedly strengthens this part of the wing so i t can bear the strain placed on i t by the attachment of the hind-wing in this area. The posterior margin of the fore-wing is heavily sclerotized to accomodate the connecting mechanism of the hind-wing, the hamuli. The hind-wing (Fig, 52A). The changes that occurred in the primitive-type wing to produce the hind-wing of Aj_ cestus are essentially the same as those that occurred in the production of the fore-wing. The main differences are: (1) the radial and costal veins are united for a short distance at their bases; (2) the median vein (M) is continuous with the distal margin of the wing, and i t is not connected to the marginal vein and has no association with i t ; (3) only one cross-vein (R-M) is present between the radial sector (RS) and the median vein (M); (4) cubitus one (Cu-^ ) is unbranched and is connected to the first anal vein (1A) by the cross-vein (Cu-A); and (5) on the base 30, of radius one (R^) are located the hamuli (Fig. 52A, 52B HAM), a row of large, posteriorly-curved spines which hold the hind- and fore-wings to-gether during flight. The axillary sclerites (Fig. 53 to 56). These are the sclerites found at the base of a l l insect wings. They facilitate the upward, downward, and rotating wing motions by presenting satisfactory articulatory surfaces for these various movements. These sclerites are collectively known as the pteralia (Snodgrass 1935). In Aj_ cestus the pteralia of each fore-wing consists of: (1) three axillary sclerites; and (2) a median plate. The first axillary sclerite (Fig, 52 1AX) is the anterior hinge plate of the wing base. Its body is supported by the anterior notal wing process of the mesonotum (Fig, 25 ANP), It extends anteriorly as a slender arm, and articulates with a humeral complex (Fig. 53) formed by the fusion of the costal (C), subcostal (SC), radial (R), and medial (M) veins, and the median plate (M-^ ). It is associated with the costal region of this complex. The second axillary (Fig. 53, 54 2AX) is the vertical sclerite articulating with the outer margin of the f i r s t axillary. Ventrally i t rotates on the fulcral wing process (Fig. 54 WP) of the pleuron, and dorsally i t is flexibly attached to the radial section of the humeral com-plex. To this sclerite is attached a small sclerite (Fig. 53 AXD) which accomodates the insertion of muscles. The third axillary (Fig. 53, 54 3AX) is an elongate sclerite articula-ting ventrally with the posterior end of the second axillary. Its distal end is associated with the anal veins (1A, 2A), and its proximal end articulates with the posterior notal wing process (Fig, 25 PNP), 31. Immediately anterior to the pleural wing process is located a free pleural sclerite (Fig. 54 P) which is associated with the axillary complex. Ventrally i t bears a small disk for muscle attachment. Snodgrass (1911) refers to this sclerite as the parapteron. It is homologous with the basalare sclerite of generalized insects (Snodgrass 1935). A large scale-like lobe is flexibly attached to the scutum immediately anterior to the wing. This is the tegula (Fig. 25 TG). It overlaps the base of the wing. The pteralia of the hind-wings (Fig. 55, 56), like that of the front, consist of three axillary sclerites and a median plate. No true tegula is present, but the lateral margins of the mesoscutellum are expanded in such a manner that they secondarily form a hood-like structure over the base of the hind-wings. The first axillary sclerite (LAX) articulates bodily with the anterior notal wing process of the metanotum. Anteriorly i t articulates with the sub-costal region of the axillary complex formed by the costal (C), sub-costal (SC), and radial (R) veins. The median vein (M) and median plate (M^ ) are not part of the axillary complex of this wing. The second axillary sclerite (2AX) articulates with the posterior margin of the first axillary sclerite, and the metapleural wing process (Fig. 56 WP). Dorsally i t is flexibly fused with the radial region of the axillary complex. It bears a small axillary disk (Fig. 55 AXD) used for muscle attachment. The third axillary sclerite (Fig. 55, 56 3AX) is an elongate sclerite associated distally with the anal veins (1A, 2A). Proximally i t articulates with the posterior notal wing process of the metanotum, and with the ELATE DC D o r s a l a s p e c t o f t h e l e f t f o r e - a n d h i n d - w i n g s (15x). D o r s a l a s p e c t o f t h e h a m u l i o f t h e l e f t h i n d - w i n g (5Cx). D o r s a l a s p e c t o f t h e l e f t m e s o t h o r a e i c w i n g a r t i c u l a t i o n (25x). L a t e r a l a s p e c t o f t h e l e f t m e s o t h o r a e i c w i n g a r t i c u l a t i o n (25x). D o r s a l a s p e c t o f t h e l e f t m e t a t h o r a c i c w i n g a r t i c u l a t i o n (35x). L a t e r a l a s p e c t o f t h e l e f t m e t a t h o r a c i c w i n g a r t i c u l a t i o n (35x). W i n g v e i n s . 1A— f i r s t a n a l v e i n ; 2A—second a n a l v e i n ; C — c o s t a l v e i n ; C t R — c o s t a l v e i n p l u s t h e r a d i a l v e i n ; C u - ^ — f i r s t b r a n c h o f t h e c u b i t a l v e i n ; C u - j ^ — f i r s t s u b s i d i a r y b r a n c h o f Cu-^; C u - ^ — s e c o n d s u b s i d i a r y b r a n c h o f C u ^ ; C u - A — c r o s s v e i n b e t w e e n Cu a n d 1A; H A M — h a m u l i ; M — m e d i a l : v e i n ; M • C u - ^ — m e d i a l v e i n p l u s t h e f i r s t b r a n c h o f t h e c u b i t a l v e i n ; I M - C u — f i r s t c r o s s v e i n b e t w e e n m e d i a l v e i n a n d t h e f i r s t b r a n c h o f t h e c u b i t a l v e i n ; 2M-Cu—second c r o s s v e i n b e t w e e n t h e m e d i u s a n d t h e f i r s t b r a n c h o f t h e c u b i t a l v e i n ; R — r a d i a l v e i n ; R ^ — f i r s t b r a n c h o f t h e r a d i u s ; R S — r a d i a l s e c t o r ; 1R-M—first c r o s s v e i n b e t w e e n r a d i a l s e c t o r a n d m e d i a l v e i n ; 2R-M—second c r o s s v e i n b e t w e e n r a d i a l s e c t o r a n d m e d i a l v e i n ; S C — s u b c o s t a ; S T — s t i g m a . A x i l l a r y a r t i c u l a t i o n s . 1AX— f i r s t a x i l l a r y s c l e r i t e ; 2AX—second a x i l l a r y s c l e r i t e ; 3 A X — t h i r d a x i l l a r y s c l e r i t e ; A X C — a x i l l a r y c o r d ; A X D — a x i l l a r y d i s k ; M-^—median p l a t e ; P ^ — p a r a p t e r o n ; P D — d i s k o f p a r a p t e r o n ; W P — p l e u r a l w i n g p r o c e s s . F i g . 52A. F i g . 5 2 B . F i g . 53. F i g . 54. F i g . 55. F i g . 56. 32. posterior end of the second axillary sclerite. The parapteron (P) is identical with the parapteron of the fore-wing, and is associated with the anterior margin of the axillary complex. It also bears a disk (PD) for muscle attachment. The Abdomen The abdomen is the portion of the insect body which contains the major viscera and the anal and genital openings. Furthermore, i t is the chief part of the body producing movements of respiration. Generally i t has ten to eleven segments in the imago stage, but this is not always constant. From embryological evidence i t has been concluded that the abdomen of the most primitive insect originally had twelve segments, but through specialization and modification the modern insect has anywhere from six to eleven segments. For descriptive purposes the author has divided the abdomen of A.  cestus in the following manner: the pregenital or visceral segments, the genital segments, and the postgenital segments. The pregenital segments. In iU cestus there are eight pregenital segments in the male, and seven in the female. The fi r s t segment (Fig. 16, 17, 28, 29 IT) has migrated anteriorly and forms the propodeal, or middle segment of the body. The sternum of this segment has been lost or has coalesced with the metathoracic sternum. The second (Fig. 57, 58 11T) is a petiole-like segment, much con-stricted at its base where i t is abruptly elbowed dorsally. Near its posterior margin i t is almost as broad as the rest of the body and is 33. elbowed posteriorly. The constriction and bending of this segment gives the abdomen a petiolate appearance. Unlike the sclerites of the general-ized abdominal segments, the tergum (11T) and sternum (11S) of this seg-ment are fused, and are differentiated by incomplete lateral sutures which terminate before reaching the base of the segment. On the lateral margins of the tergum at the posterior elbow are located the second aMominal spiracles. The location of these spiracles are significant morphological characters used by present-day hymenopterists in the construction of keys to Ichneumonid genera. The base of this segment bears three bulbous condyles, one dorsal and two lateral, which articulate with the propodeal condyles extending into the posterior thoracic aperture. The third, fourth, fifth, sixth, and seventh abdominal segments of both sexes are very similar in size and shape. Each has a broad tergum (HIT, 1VT, VT, V1T, V11T) which i s continuous with a semi-sclerotic sternum (HIS, 1VS, VS, VIS, V11S). The latter, which is much softer and more pliable than the tergum, shows signs of having lateral divisions which are the homologues of the pleural sclerites of the primitive insect segment. The terga of the pregenital segments and that of the eighth segment each bear a pair of spiracles near their lateral margins. The majority of these are hidden due to an increased telescoping of the posterior segments. Near the anterior margin of the third tergum (HIT) is located a pair of broad, deep, oblique quadrate pits. The anterior margin of the fourth abdominal tergum bears a broad black band which is used to help identify this species from its close relatives. In the series of specimens examined by the author this band was absent in some teneral males. This may be due to colour variation 34. c a u s e d b y e n v i r o n m e n t a l f a c t o r s s u c h a s t e m p e r a t u r e , h u m i d i t y , a n d l i g h t w h i c h a r e i n f l u e n t i a l d u r i n g t h e p r o d u c t i o n o f p i g m e n t a t i o n i n i n s e c t s ( W i g g l e s w o r t h 1939). The g e n i t a l s e g m e n t s . These a r e t h e a b d o m i n a l segments w h i c h a r e c l o s e l y a s s o c i a t e d w i t h t h e g e n i t a l o p e n i n g s . T h e i r appendages a n d o u t g r o w t h s f o r m t h e p r i n c i p a l c o p u l a -t o r y o r g a n s o f b o t h s e x e s . I n t h e male o f t h i s s p e c i e s t h e o n l y segment r e s p o n s i b l e f o r t h e male g e n i t a l i a i s t h e n i n t h . The f e m a l e g e n i t a l i a a r e c o m p o s i t e s t r u c t u r e s w h i c h d e v e l o p f r o m t h e e i g h t h a n d n i n t h s e g m e n t s . I n t h i s r e s p e c t t h e g e n i t a l s egments o f c e s t u s a r e s i m i l a r t o t h o s e o f t h e m a j o r i t y o f g e n e r a l i z e d i n s e c t s . The p o s t g e n i t a l segments ( F i g . 57, 5$ I X and X T ) , These g e n e r a l l y i n c l u d e t h e t e n t h a n d e l e v e n t h a b d o m i n a l segments when p r e s e n t . I n Aj_ c e s t u s . t h e l a t t e r i s a b s e n t , a n d t h e f o r m e r i s much r e d u c e d . I n b o t h s e x e s t h e t e n t h t e r g u m i s f u s e d w i t h t h e n i n t h t e r g u m a n d f o r m s w i t h i t a s y n t e r g u m a s d e f i n e d b y P e c k (1937). I n t h e f e m a l e t h e membrane i m m e d i a t e l y v e n t r a l t o t h e a n a l a p e r t u r e has a s m a l l s e m i - s c l e r o -t i z e d a r e a w h i c h b e a r s s e t a e . T h i s i s p e r h a p s t h e remnant o f t h e t e n t h s t e r n u m . I n t h e membrane b e t w e e n t h e t e r g u m a n d s t e r n u m o f t h i s segment a r e l o c a t e d o v a l - s h a p e d appendages (SOC) w h i c h a r e t h e homologues o f t h e s o c i i o f t h e l e p i d o p t e r o u s i n s e c t s . These a r e e x c e l l e n t l a n d m a r k s f o r t h e p o s t g e n i t a l s e g m e n t s . The G e n i t a l i a As p o i n t e d o u t a b o v e , t h e s e a r e t h e c o p u l a t o r y o r g a n s o f t h e ma le a n d f e m a l e w h i c h a r e d e v e l o p e d f r o m t h e g e n i t a l segments ( F i g . 57 V 1 1 T , V111T, V 1 1 S , V 1 1 1 S ; F i g . 58 V H T , V111T, V 1 1 S ) . C o n s i d e r a b l e harmony e x i s t s 35. among authors concerning the development of the female genitalia, but discord and controversy have developed over the evolution of the male genitalia. The present author has followed the work of Snodgrass (1935) in his discussion of the female organs, and that of Peck (1937) in the discussion of the male organs. The female genitalia. From studies by Snodgrass (1935) fairly good evidence substantiates his conclusion as the the derivation of the female genitalia. In most pterygote insects the ovipositor shaft, sheath, and basal apparatus are apparent derivatives of the primitive insect gonopophyses, styli, and coxopodites of the genital segments. The female genitalia (Fig. 59, 60) of Aj. cestus consists of a long ovipositor attached to a basal apparatus and enclosed in an ovipositor sheath. The ovipositor is an elongate shaft composed of a ventral and dorsal pair of valvulae (1VL, 2VL) which are homologous to the gonopophyses of primitive insects. The dorsal valves are fused in a single shaft which is united to the ventral pair by a tongue-and-groove system (Fig. 60). There are two channels formed by these shafts, the lower being the egg tube (ET). The apex of the ovipositor is lance-shaped, and bears strong lateral serrate ridges for penetration of the host skin. The base of the second v a l v u l a e bears a large knob-shaped median process (Fig. 59 RP) called the rotary process by Bucher (1948). The bases of the first and second valvulae a r e attached by rami (Rl, R2) to the basal apparatus. The r a m i of the first valvulae b e a r a pair of a p o p h y s e s (A) for muscle attachment. The basal apparatus 36. c o n s i s t s o f a p a i r o f s m a l l t r i a n g u l a r p l a t e s ( 1 V L F ) a r t i c u l a t e d b y t h e i r p o s t e r i o r v e n t r a l c o r n e r s t o a s e c o n d p a i r o f e l o n g a t e p l a t e s ( 2 V L F ) , a n d b y t h e i r p o s t e r i o r d o r s a l c o r n e r s t o t h e n i n t h t e r g u m . These p l a t e s a r e t e r m e d t h e f i r s t a n d s e c o n d v a l v i f e r s b y S n o d g r a s s (1935), a n d a r e h o m o l o -gous t o t h e c o x o p o d i t e s o f t h e p r i m i t i v e e i g h t h a n d n i n t h s e g m e n t s . The s e c o n d v a l v i f e r s a r e e l o n g a t e d p o s t e r i o r l y i n t o s h e a t h - l i k e v a l v u l a e w h i c h e n c l o s e t h e f i r s t a n d s e c o n d v a l v u l a e . T h e s e a r e t h e t h i r d v a l v u l a e o f g e n e r a l i z e d i n s e c t s , a n d a r e d e r i v a t i v e s o f t h e s t y l i o f t h e c o x o p o d i t e s . They a r e s e n s o r y i n f u n c t i o n . The s t e r n a o f t h e e i g h t h a n d n i n t h s e g m e n t s , f r o m w h i c h t h e f e m a l e g e n i t a l i a a r e d e r i v e d , a r e a b s e n t . The s t e r n u m o f t h e s e v e n t h segment ( F i g , 58 VULS) f o r m s a s u b - g e n i t a l p l a t e . The t e r g u m o f t h e e i g h t h segment (V111T) i s e l o n g a t e d v e n t r a l l y a n d f o r m s a s e m i - s h e a t h f o r t h e f o l l o w i n g a b d o m i n a l p a r t s . The n i n t h t e r g u m ( I X a n d X T ) i s c o a l e s c e d w i t h t h e t e n t h t e r g u m , a n d t h e t w o a r e c l o s e l y a s s o c i a t e d w i t h t h e f e m a l e c o p u l a t o r y a p p a r a t u s . The m a l e g e n i t a l i a . I n i n s e c t s t h e m a l e g o n o p o r e , o r g e n i t a l o p e n i n g , i s g e n e r a l l y a s s o c i a t e d w i t h t h e n i n t h a b d o m i n a l segment w h i c h i s d i r e c t l y r e s p o n s i b l e f o r t h e f o r m a t i o n o f t h e r e s u l t i n g m a l e g e n i t a l i a . A u t h o r i t a t i v e a u t h o r s a p p e a r t o be i n s t r o n g d i s a g r e e m e n t c o n c e r n i n g t h e e x a c t e v o l u t i o n a r y d e v e l o p m e n t o f t h e h y m e n o p t e r a n m a l e o r g a n s , a n d , a s a r e s u l t , a v a r i e t y o f t e r m i n o l o g y h a s a p p e a r e d . The two most p r o n i i n e n t c o n t r o v e r s i a l p a p e r s o n t h i s t o p i c a r e t h o s e o f P e c k (1937) a n d S n o d g r a s s (1941)• P e c k u p h o l d s t h e t h e o r y t h a t t h e m a l e o r g a n s o f t h e H y m e n o p t e r a , e s p e c i a l l y t h o s e o f t h e I c h n e u m o n i d a e , a r e d e r i v a t i v e s o f t h e p r i m i t i v e 37. c o x o p o d i t e a p p e n d a g e s . S n o d g r a s s , o n t h e o t h e r h a n d , h o l d s t o h i s o r i g i n a l t h e o r y (1935) t h a t t h e m a l e c o p u l a t o r y o r g a n s i n t h e H y m e n o p t e r a d e v e l o p f r o m t h e c o n j u n c t i v a l membrane b e t w e e n t h e s t e r n a o f t h e e i g h t h a n d n i n t h s e g m e n t s . B o t h w r i t e r s g i v e s u b s t a n t i a l e v i d e n c e f o r t h e i r c o n c l u s i o n s , b u t , b e c a u s e t h e e v i d e n c e i s c o n t r a d i c t o r y , t h e p r o b l e m r e -m a i n s i n a c o n t r o v e r s i a l s t a t e . Because P e c k r e s t r i c t e d h i s s t u d y t o t h e I c h n e u m o n i d a e , t h e f a m i l y t o w h i c h c e s t u s b e l o n g s , t h e a u t h o r f i n d s i t c o n v e n i e n t t o a d o p t h i s t e r m i n o l o g y , a n d u n t i l f u r t h e r e v i d e n c e i s g i v e n t o d i s p r o v e one o f t h e s e c u r r e n t t h e o r i e s , i t i s i m p o s s i b l e t o s t a t e t h e h o m o l o g i e s o f t h e hymenop-t e r a n m a l e g e n i t a l i a . T h e r e f o r e , t h e - f o l l o w i n g d i s c u s s i o n o f t h e m a l e c o p u l a t o r y o r g a n s i n c e s t u s i s p u r e l y a n a m i n g a n d d e s c r i p t i o n o f t h e v a r i o u s p a r t s . I n t h i s s p e c i e s t h e m a l e g e n i t a l i a ( F i g . 6 l , 62) i s composed o f f o u r m a i n p a r t s : a b a s a l r i n g , a n o u t e r p a i r o f c l a s p e r s , a n i n n e r p a i r o f c l a s p e r s , a n d a n i n t r o m i t t e n t o r g a n . The b a s a l r i n g , o r g o n o c a r d o ( G C ) , i s l o o s e l y a t t a c h e d b y membrane t o t h e n i n t h segment i m m e d i a t e l y p o s t e r i o r t o t h e g e n i t a l p l a t e ( F i g . 57 1 X S ) . The o u t e r c l a s p e r s , o r g o n o f o r c e p s ( F i g . 6 l , 62 G F ) , a r e b r o a d e l o n g a t e s c l e r i t e s a t t a c h e d b y membrane t o t h e p o s t e r i o r m a r g i n o f t h e g o n o c a r d o . D o r s a l l y t h e y c o a l e s c e a l o n g t h e a n t e r i o r p a r t o f t h e i r d o r s a l m a r g i n s , a n d a r e c o n t i n u o u s / m e m b r a n e t e t h e d o r s a l s u r f a c e o f t h e i n t r o m i t t e n t o r g a n , t h e aedeagus ( A E D ) . T h e i r a n t e r i o r v e n t r a l a n g l e s i a r e e x t e n d e d a n t e r i o r l y t o f o r m a p a i r o f a p o p h y s e s , t h e g o n o s t i p : L a l arms ( G S T A ) , f o r m u s c l e a t t a c h m e n t . I m m e d i a t e l y p o s t e r i o r t o t h e s e a rms t h e g o n o f o r c e p s a r e c o n t i n u o u s w i t h t h e i n n e r c l a s p e r s , t h e b a s i v o l s e l l a ( B V ) . 38. These are broad plates which are invaginated into the interior cavity formed by the outer claspers. Their dorsal margins are reinforced by a heavy sclerotic bar, the basivolsellar strut (VSTR) which prevents bending of the basivolsella during copulatory activities. Distally the basivolsella bears a pair of hook-like sclerites used to grasp and hold taut the conjunctival membrane of the female so that the aedeagus can be inserted into the female gonopore and retained there. The more dorsal sclerite, the gonalacinia (GL), is a separate unit which articulates on the posterior dorsal angle of the basivolsella. The ventral sclerite, the distivolsella (DV), is an elongation of the posterior ventral margin of the basivolsella curved back on itself giving i t a hood-like appearance. The intromittent organ, or aedeagus (AED), consists of a pair of elongate bars connected by membrane to the dorsal margins of the gono-forceps and dorsal margins of the basivolsella. Dorsally they are conti-nuous for the most part, and ventrally they coalesce at their bases. Distally they curve ventrally and are slightly expanded. Anteriorly they extend far into the body cavity as a pair of apophyses (Fig. 6l APA) for muscle attachment. A pair of lateral extensions, the ergots (ERG), at the base of these apophyses, serve as pivots for the intromittent organ during coition. PLATE X F i g * 57. L a t e r a l a s p e c t o f t h e m a l e abdomen. F i g . 58. L a t e r a l a s p e c t o f t h e f e m a l e abdomen. F i g . 59. L o n g i t u d i n a l s e c t i o n o f t h e f e m a l e g e n i t a l i a . F i g . 60. C r o s s s e c t i o n o f t h e f e m a l e o v i p o s i t o r . F i g . 6 1 . L o n g i t u d i n a l s e c t i o n o f t h e m a l e g e n i -t a l i a . F i g . 62. V e n t r a l a s p e c t o f t h e m a l e g e n i t a l i a . A—apodeme o f t h e f i r s t v a l v u l a j A E D — a e d e a g u s ; A P A : — a p o p h y s i s o f t h e a e d e a g u s j B V — b a s i v o l s e l L a ; D V — d i s t o v o l s e l l a ; E R G — e r g o t o f t h e a e d e a g u s j E T — e g g t u b e ; G C — g o n o c a r d o ; G F — g o n o f o r c e p s ; G L — g o n o l a c i n i a ; GSTA:—gono-s t i p i a l a r m ; R ^ — r a m i o f t h e f i r s t v a l v u l a ; S2— r a m i o f t h e s e c o n d v a l v u l a ; R P ~ r o t a r y p r o c e s s ; 11S, Ills, 1VS, V S , V I S , V11S, V111S, 1 X S — s e c o h d , t h i r d , S O C - - s o c i i ; f o u r t h , f i f t h , s i x t h , s e v e n t h , e i g h t h , a n d n i n t h a b d o m i n a l s t e r n a ; / L I T , 111T, 1VT, V T , V1T, V11T, V111T, 1XT, X T — s e c o n d , t h i r d , f o u r t h , f i f t h , s i x t h , s e v e n t h , e i g h t h , n i n t h , a n d t e n t h a b d o m i n a l t e r g a ; 1 V L— f i r s t v a l v u l a ; 2VL— s e c o n d v a l v u l a ; 3 V L — t h i r d v a l v u l a ; 1VLF— f i r s t v a l v i f e r ; 2VLF—second v a l v i f e r ; V S T R — b a s i v o l s e l l a r s t r u t . 39. Summary The author has made a study of the external anatomy of Aoplus cestus (Cresson), an Ichneumonid parasite of the oak looper, Lambdina somniaria (Hulst), and of the hemlock looper, lambdina fiscellaria lugubrosa (Hulst), The various parts are described, and where possible an attempt has been made to homologize them with the parts of more generalized and primitive insects. A detailed description is given of: (1) the exoskeleton and endoskeleton of the head and its appendages; (2) the exoskeleton and endo-skeleton of the three thoracic segments; (3) the abdomen; (4) the legs; (5) the wings and axillary sclerites; and (6) the male and female genitalia. Sixty-two illustrations accompany the text. 40 L i t e r a t u r e C i t e d B r o w n , W. J. 1949. The R o l e o f M o r p h o l o g y i n S y s t e m a t i c s . C a n . E n t . 82(12): 299-303. B u c h e r , G . E . 1948. The Anatomy o f Monodontomerus d e n t i p i s B o h . , a n Entomophagous C h a l c i d . C a n . J. R e s . D , 26: .230-281. C o m s t o c k , J. H . , a n d A . B . C o m s t o c k . 1899. A M a n u a l o f t h e S t u d y o f I n s e c t s . The C o m s t o c k P u b l i s h i n g C o . , I t h a c a , N . Y . C o m s t o c k , J. H . , a n d J. G . Needham. 1898. The W i n g s o f I n s e c t s . A m . N a t . 32. C o m s t o c k , J. H . , a n d J. G . Needham. 1899. The W i n g s o f I n s e c t s , A m . N a t . 33. C o m s t o c k , J. H . 1936. An I n t r o d u c t i o n t o E n t o m o l o g y . 8th E d . R e v i s e d . Comstock P u b l i s h i n g C b , I n c . , I t h a c a , N . Y . C r a m p t o n , G . C . 1917. A C o m p a r i s o n o f t h e Neck a n d P r o t h o r a c i c S c l e r -i t e s . T r a n s . Am. E n t . S o c . 52: 199-248. P i s . 10-17. C r e s s o n , E . T . 1878. D e s c r i p t i o n o f I c h n e u m o n i d a e , C h i e f l y f r o m t h e P a c i f i c S l o p e o f t h e U n i t e d S t a t e s a n d B r i t i s h N o r t h A m e r i c a . P r o c . A c a d . N a t . S c i . P h i l a d e l p h i a , p . 353. ( D e s c r i p t i o n . ) F e r r i s , G . F . 1928. P r i n c i p l e s o f S y s t e m a t i c E n t o m o l o g y . S t a n f o r d U n i v e r s i t y P u b l i c a t i o n s . U n i v . S e r . B i o l . S c i . 5(3): 101-269. F o r b e s , T . M . 1925. The H y p o t h e t i c a l W i n g o f t h e H y m e n o p t e r a . A n n 0 E n t . S o c . Am. 18:: 22. Imms, A . D . 1937. R e c e n t A d v a n c e s i n E n t o m o l o g y . 2nd E d . J. & A . C h u r c h i l l , L o n d o n . M a c G i l l i v r a y , A . D . 1906. A S t u d y o f t h e W i n g s o f t h e T e n t h r e d i n i d a e , a S u p e r f a m i l y o f H y m e n o p t e r a . P r o c . U . S . N a t l . M u s . 29: 569-654. 41. P e c k , 0. 1937. The M a l e G e n i t a l i a i n t h e H y m e n o p t e r a ( I n s e c t a ) , E s p e c i a l l y t h e F a m i l y I c h n e u m o n i d a e . C a n . J . R e s . D , 15: 221-274. R i e g e l , G . T . 1948. The W i n g s o f B r a c o n i d a e ( H y m e n o p t e r a ) . A n n . E n t . S o c . Am. 41: 439-449. R o h w e r , S . A . , a n d A . B . G a h a n . 1916. H o r i s m o l o g y o f t h e Hymenopte rous W i n g . P r o c . E n t . S o c . W a s h . 18 (1): 20-76. 3 P i s . R o s s , H . H . 1936. The A n c e s t r y a n d W i n g V e n a t i o n o f t h e H y m e n o p t e r a . A n n . E n t . S o c . Am. 29: 99. S n o d g r a s s , R . E . 19H. The T h o r a x o f t h e H y m e n o p t e r a . P r o c . U . S . N a t l . M u s . 39:: 37-91. 16 P i s . S n o d g r a s s , R . E . 1935. P r i n c i p l e s o f I n s e c t M o r p h o l o g y . M c G r a w - H i l l Book C o . I n c . , N . Y . S n o d g r a s s , R . E . 1941. The M a l e G e n i t a l i a o f H y m e n o p t e r a . S m i t h s . M i s c . Coll. 99 (14). 33 P i s . S n o d g r a s s , R . E . 1942. The S k e l e t o - M u s c u l a r M e c h a n i s m o f t h e Honey B e e . S m i t h s . M i s c . C o l l . 103(2). Torre^-Bueno , J . ' R . 1937. A G l o s s a r y o f E n t o m o l o g y . B r o o k l y n E n t o m o -l o g i c a l S o c i e t y , B r o o k l y n , N . Y . Townes , H . K . J r . 1944. A C a t a l o g u e a n d R e c l a s s i f i c a t i o n o f t h e N e a r c t i c I c h n e u m o n i d a e ( H y m e n o p t e r a ) . Mem. Am. E n t . S o c . 11. W a l k e r , E . M . 1932. P r o g n a t h i s m a n d H y p o g n a t h i s m i n I n s e c t s . C a n . E n t . 64(10): 223-229. W i g g l e s w o r t h , V . B . 1939. The P r i n c i p l e s o f I n s e c t P h y s i o l o g y . M e t h u e n & C o . L t d . , L o n d o n . 

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