37S ME. WALTER WESCHE ON THE GENITALIA OF 



highly modified, also much simplified. The labrum or upper lancet is only equalled in 

 simplicity by that part in the Culicida?, while the hypopharynx is in an atrophying 

 condition in Glossina. In Stomoxys the male genitalia are relatively small, though in 

 Glossina they are highly developed and modified, yet both are simplifications of the 

 Muscid type, owing to the abortion and fusing of the appendages of the theca, the 

 spinus, genital palpi, and interior hooks. There is no extrusile ovipositor in Glossina, 

 but in Stomoxys there are indications that at some period it resembled that of 

 Musca domestica \ the joints appear to be there, but in a fused condition. I spent a 

 considerable time unsuccessfully endeavouring to extend the organ. There is also 

 simplification in the number of receptacula, which is always two in this group. 



Analogy in the Mammalia. — In addition to what I have advanced in favour of the 

 theory of the intimate connexion between the growth of the genitalia and of the 

 mouth-parts, it may be pointed out that there are analogies in the Mammalia, where 

 the efi"ects of excision of the genitalia on the throat and voice, as well as beard, of 

 the male are common knowledge. 



Summary of the mam argument. — I have now shown : (1) That the male genitalia 

 and the mouth -armature are on the same general plan, of a central perforated organ 

 surrounded by aculeate and sensory or possibly sensory appendages. (2) That they 

 coincide in many details of structure and arrangement. (3) That the male and female 

 genitalia are homologous. (Jj) That the male armature, the ovipositor, and the mouth- 

 parts have a central mechanism (double apodemes, apodeme of ovipositor, fulcrum or 

 submentum), which guides or governs the whole, or traces or remains of such a part. 



(5) That the application of an hypothesis founded on the above data accounts for the 

 hitherto unexplained failure of the male mouth-parts in the Culicida3 and the Tabanidae. 



(6) That an intimate connexion is known to exist between the male genitalia and 

 the throat, voice, and the hairy appendages of the mouth in the Mammalia. 



Ancestral form of the Arthropoda. — Further, I am informed by Mr. H. M. Bernard, 

 F.L.S., &c., that the idea that genitalia and mouth-parts are homologous is not new ; 

 the hypothesis has been advanced that, in a primitive ancestral form of the Arthropoda, 

 these mechanisms were formed by adaptations of the legs of the end segments. 



My opinions are arrived at by a close study of the mouth and genitalia of the 

 principal families in Diptera, and almost wholly by methods of comparative anatomy. 

 My arrival at what is practically the same conclusion, by an enquiry comparatively very 

 narrow iti its scope, being confined to a single Order, is evidence in favour of this 

 hypothesis. 



Weighing these facts, I submit that there is much evidence in favour of my main 

 thesis, which may be formulated thus : — 



Formula. — The external appendages of both extremities in Insecta are derived from 

 two oigans of the character of maxillae, and all the variations of the parts are 

 adaptations of these organs. 



