AND THEIR HOMOLOGY WITH THE GENITALIA IN DIPTERA. 239 



plications at the extremities of an insect have been produced 

 by gradual changes in the more simple appendages. 



(i) Forcipes inter lores. — These are represented by two un- 

 symmetrical pieces, the one on the left having the point twisted 

 round like a corkscrew, the other furcate ; their upper ends 

 connect by means of a hyaline membrane, while their bases 

 join with a complicated structure, consisting of a number of 

 plates and membranes, with extremely elaborate muscular 

 attachments, which form the containing apparatus of the 

 spermatophore. This portion of the containing apparatus seems 

 homologous with that part of the theca which in the Muscidae 

 supports the titdlator , forcipes interiores, and the palpi genitalium. 

 This view is strengthened by the situation of the remnant of the 

 palpus. 



(k) Palpi genitalium. — The organs are aborted, but the site 

 is marked on the left side, on a piece which is soldered to the 

 left forceps, by a number of sensory hairs. Comparing it with 

 remnants of palpi in other parts and in other insects, I have no 

 hesitation in identifying this. The absence of a similar vestige 

 on the right side is accounted for by the situation of the " cover " 

 (Fig. 6), wdiich would quite shut off this side from any function. 



(m) TJie great apodemes. — I have found on each side of the 

 theca two small islands of chitin, surrounded by a sea of hyaline 

 membrane. They appear to be without any function, and are 

 nearly suboval plates tapering to points. From their structure 

 and from their position, I consider these as the atrophied 

 remains of the apodemes, whose function is so important and 

 whose presence is so constant in most insects. Their disuse 

 has been brought about by the changes already discussed 

 (Figs. 1, 2, m). 



(o) Sacculus ejacidatorius. — This organ in the Muscidae is 

 membranous, but in the Tipulidae it has a chitinous structure, 

 .and suggests that it has its counterpart in the very complicated 

 Journ. Q. M. C., Series II.— No 62 18 



