On the Development of the Male Genitalia and the Efferent Genital Ducts in Lepidoptera

On the Development of the Male Genitalia and the Efferent Genital Ducts in Lepidoptera. By Dev Raj Mehta, M.Sc, Ph.D. (Cantab.) University Scholar of the Government of the Punjab. From the Department of Zoology, Cambridge. With 18 Text-figures. CONTENTS. PAGE INTRODUCTION .......... 35 MATEBIAL AND TECHNIQUE . .37 NOMENCLATURE 39 DESCRIPTION OF THE GENITAL ORGANS IN THE IMAGO . .39 DEVELOPMENT : (a) Genitalia 41 (6) Efferent Genital Ducts ....... 51 SUMMARY 59 REFERENCES .......... 60 INTRODUCTION. ONLY in a few groups of insects has the homology of the external genitalia been determined by investigations into the development of these organs. During the concluding part of the last century two conflicting views were held regarding the nature of gonapophyses. Accord- ing to Lacaze-Duthiers (1849-53), Grassi (1889), and Haase (1889) they are integumental outgrowths corresponding to the ' styloid' processes (' Griffel') which are present on the abdomen and inserted at the bases of the legs in such generalized insects as the Thysanura. On the other hand, Weismann (1864), Kraepelin (1873), Dewitz (1875), Huxley (1877), and Cholodkovsky (1891a) showed that the gonapophyses are comparable to the true D2 36 DBV RAJ MEHTA ambulatory legs. In this connexion Kraepelin (1873), Dewitz (1875), and others described these appendages as arising from imaginal discs, and Wheeler (1893) showed that there exists a direct continuity of the embryonic appendages with the Zander (1900,1901,1903) actually described the development of the penis and the gonapophyses ('valvae') in the post- embryonic stages of Hymenoptera, Trichoptera, and Lepido- ptera from paired rudiments or buds on the ninth abdominal segment. This formed a basis for later work on these lines, and his conclusions were largely confirmed in certain other insect orders. In this connexion may be mentioned the work of Muir (1915, 1918) and Singh-Pruthi (1924) on Coleoptera, Christo- phers and his collaborators (1922, 1926) on Diptera, Kershaw and Muir (1922), Singh-Pruthi (1924) and George (1929) on Homoptera and Zygoptera respectively. Verson and Bisson (1896) also referred to the development of the male genitalia in Bombyx mori Linn, in their exten- sive memoir on the origin and nature of the efferent genital ducts in this species. Their conclusions, however, were criticized by Zander (1903), and his work, since then, is the only compre- hensive account to which reference could be made for determin- ing the homologies of the elements composing the insect genitalia. It has also been realized that the mode of origin of the 'valvae' as described by Zander (1903) is open to question (Singh-Pruthi, 1924), and his conclusions differ from those of his predecessors (Verson and Bisson, 1896, and others). The development of the posterior abdominal segments and their appendages in Lepidoptera need further reinvestigation, because Zander's observations (1903) on these lines, though conclusive, were not confirmed by subsequent workers. It therefore is desirable that the whole problem should be revised in the light of existing knowledge of orders other than the Lepidoptera. With this in view I have studied the development of the male genitalia in the following Lepidoptera, viz. Hepialus lupulinus Linn., Pieris rapae Linn., Earias fabia Stoll., and Bombyx mori Linn., as representatives of the sub- GENITALIA IN LEPIDOPTERA 87 order Homoneura and the super-families Papilionina, Noctuina, and Notodontina respectively. In this account I have also included a general description of the development and nature of the efferent genital ducts in the above forms. Much confusion prevails on this subject, and I have discussed at length the existing views on it throughout the whole class, supporting my arguments with the conditions which I find in the Lepidoptera mentioned above. It is with great pleasure that I express my indebtedness to Mr. L. E. S. Eastham, my supervisor of research studies, for suggesting this problem and taking a keen interest in the pro- gress of this research. I am also thankful to Dr. A. D. Imms for various valuable suggestions in preparing the manuscript for publication. To Professor J. Stanley Gardiner I am much indebted for providing me with every facility for work in the Zoological Laboratory, Cambridge. The material for this work was obtained locally and was partly sent to me from India. In this connexion, I wish to express my sincere thanks to Mr. M. Afzal Husain, Entomologist to the Government of the Punjab, for supplying me with the developmental stages of the silk-worm moth Bombyx mori Linn. This investigation was conducted during the tenure of a University Scholarship awarded by the Government of the Punjab, India. The grant made by the State is gratefully acknowledged. MATEBIAL AND TECHNIQUE. The common British forms such as Pieris rapae Linn, and Hepialus lupulinus Linn, were reared in the laboratory. The developmental stages of Earias fabia Stoll. and the silk-worm moth Bombyx mori Linn, were received from the Entomological Section, Department of Agriculture, Punjab, by the courtesy of the authorities. The specimens were fixed in Bouin's picro-formol and Carnoy's fluids. Eeal difficulty was experienced in sectioning the last larval and pupal stages of large forms such as Hepialus and Bombyx, on account of the thick outer chitinous cuticle and 38 DEV EAJ MBHTA the amount of air usually retained in the pupae. For this I have devised a modification of Boycott's1 usual clove-oil celloidin method. It may be here recalled that his method consists in double-embedding of the tissue first in celloidin followed by paraffin, and is suitable only for smaller organisms. Below I give my modification of his method, which I pre- sume will be found useful for sectioning the bigger forms which are apt to retain large quantities of air in the body cavity. After proper dehydration and clearing in clove oil the object is kept in each grade of celloidin solution for twenty-four hours, and finally left in the thick solution for a couple of days. This immersion may take a number of days, according to the size of the tissue. It is of great advantage to prick small holes on the pupal covering to ensure the complete penetration of celloidin. After this treatment the material is transferred to a vial containing chloroform, and after the celloidin has set the outer layer of celloidin is removed from around the object. It is at this stage freed from all traces of clove oil by keeping it immersed in chloroform from one to two days, according to the bulk of the specimen. The material is now ready for embedding in paraffin, where it is kept preferably for five to six hours. It is best to be sure now that every trace of chloroform is eliminated from the tissue. This can be easily tested by pouring the melted paraffin over some water in the basin. The presence of any chloroform can be detected by the formation of peculiar crystal-shaped blocks of paraffin. During the embedding of the pupal stages of Lepidoplera it has been found essential to get rid of any air bubbles in the specimen. This is successfully accomplished by keeping it in melted paraffin for about an hour in Hearson's vacuum embedding oven. Having ensured this and the complete penetration of paraffin, the block is made in the usual way and cut into 6-8 fi thick serial sections. For staining I have used Heidenhain's iron haemotoxylin in all my preparations. Eosin can also be employed as a counter- stain in some cases. 1 Cited in Bolles Lee's 'Microtomist's Vade-Mecum' (1928). GBNITALIA IN LEPIDOPTEBA 39 NOMENCLATURE. The following is a list of names adopted in this work to denote the different parts of the male genitalia in Lepidoptera. Uncus (Gosse, 1883). This forms the dorsal process of the tenth segment. The latter usually remains membranous and retracted below the ninth tergite. The anal tube lies just below the uncus and sometimes projects some distance away from it. Tegumen (Buchanan White, 1876). This term is now employed to denote the dorsal part of the ninth segment. Vinculum (Pierce, 1909). Saccus in part (B. Baker, 1891). This is a ventral chitinized band which represents the sternite of the ninth segment. Valvae (Burmeister, 1832). These are paired clasping organs which basally articulate with the vinculum and lie in a latero-ventral position. Gnathos (Pierce, 1909). This term indicates a sub-anal structure hinged basally to the uncus, and represents the ventral process of the tenth Anellus (Pierce, 1909). It is a cone-like tube or a small, more or less triangular plate which is ventrally supported by the vinculum and on either side by the valvae. It is often extended into lateral process called the 'Anellus lobes'. DESCRIPTION OF THE GENITAL ORGANS IN THE IMAGO. Text-fig. 1 illustrates the internal reproductive organs and the external genitalia in Pieris rapae Linn. The testes (Tes) are lodged close to the alimentary canal (Gut) and just underneath the fifth and sixth abdominal tergites, more or less 40 DEV RAJ MEHTA in a dorso-lateral position. They are fused in the median line and enclosed in a common membrane (Text-fig. 2). From the testes arise a pair of genital ducts, the vasa deferentia (Text- figs. 1-2, Vrf), which dilate distally to form the vesiculae seminales (Sv). The latter are situated on the seventh segment VT VI T VII. T VIII T Tts Ag VSt. V, D\ej. Val TEXT-FIG. 1. Diagrammatic, showing the internal reproductive organs and the external genitalia in Pieris rapae Linn. LETTERING FOB ALL TEXT-FIGS. A, anal tube; Ag, accessory gland; An.l, anellus lobes; Ct, chitinous cuticle; D.ej, ductus ejaculatorius; Dv, dorsal vessel; Ej.d', ductus ejaculatoriua duplex; Ej.d", ductus ejaculatorius simplex; Oc, genital cavity; tin, gnathos; Out, intestine; Hyp, epidermis (hypo- dermis); P, penis; PI, penis lobe; Pp, penis pouch; Pup.ct, pupal chitin; Sv, vesicula seminales; Seg, segment; St, sternite; T, tergite; Tes, testes; Tg, tegumen; Tr, trachea; U, uncus; Val, valve; VI, valvae lobe; Vd, vas deferens; Fm, vinculum; I-X, the different abdominal segments.

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