No. 64] DIPTERA OF CONNECTICUT : MORPHOLOGY 79 



the ninth segment behind it could readily become reduced and unite 

 with the other terminal segments to form a proctiger (in which the 

 only important features are the sensory cerci, and the anal opening 

 for the discharge of the faeces). In the lower Diptera, on the other 

 hand, the proctiger of the male is usually smaller and more incon- 

 spicuous than that of the female, and this also holds true of the male 

 rhagionid (leptid) shown in Fig. 12, A, in which the proctiger is more 

 reduced than that of the female rhagionid shown in Fig. 9, F. 



The stages in the development of the proctiger or "anal seg- 

 ment" may be illustrated by the series of female Diptera shown in 

 Fig. 9, A,F and E. Thus in the female tipulid Clytocosmus shown in 

 Fig. 9, A, the comparatively well developed ninth and tenth segments 

 are distinct, and the cercus-bearing eleventh segment (with which 

 the anus-bearing telson has united) is apparently represented largely 

 by the distinct, though small sclerites at the bases of the cerci, ce. In 

 the female rhagionid (leptid) Chrysopilus shown in Fig. 9, F, the 

 cerci-bearing eleventh segment has united with the reduced tenth seg- 

 ment to form a composite apparent tenth "segment" bearing the cerci, 

 ce, and still distinct from the ninth segment in front of it. In the 

 female housefly shown in Fig. 9, E, the cercus-bearing composite "seg- 

 ment" (representing the united tenth and eleventh segments, with the 

 telson) tends to merge with the ninth segment, and in the female 

 Diptera shown in Fig. 9a, B, C and D, the segments behind the eighth 

 have become iiidistinguishably united to form a cercus-bearing proc- 

 tiger or "anal segment" (labelled pgi' in the figures). 



A suranal or supra-anal plate, called the epiproct, may occur in 

 the dorsal region of the "anal segment" (above the anal opening), 

 and a subanal plate, called the hypoproct, may occur in the ventral 

 region of the "anal segment" (below the anal opening), but the exact 

 homologies of these sclerites and the homology of the sclerite called 

 the postgenital plate in the females of the lower Diptera studied by 

 Gerry (1932) have not been definitely determined. It is possible 

 that the paraprocts, or parapodial plates of lower insects, may enter 

 into the composition of the plates below the anus in certain Diptera, 

 but this can be determined only after these parts in the Diptera have 

 been compared with those of the lower insects, and it is evident 

 there is a decided need of more extensive and detailed studies of the 

 terminal abdominal structures of both sexes, in the Diptera. 



The cerci are usually better developed in the females than in 

 the males of the lower Diptera, excepting in the dolichopodids, in 

 which the cerci of the males may become enormously developed. The 

 cerci may be two-segmented in the females of some Nematocera 

 (mycetophilids) and Braclwcera (stratiomyids). but they are usually 

 composed of but one segment in the males of these insects; and in 

 most of the Cyclorrhapha (excepting a few syrphids) the cerci are 

 composed of but one segment in both sexes, those of the males being 

 frequentlv as large as, or even larger than, those of the females. 

 The modifications of the cerci will be described under the discussion 

 of the terminal abdominal structures of both sexes of the Diptera. 



