No. C4] DIPTERA OF CONNECTICUT: MORPHOLOGY 89 



tendency (or genetic factor) present, tliough latent, in most male 

 Diptera. but finding opportunity for expression (or the right genetic 

 conditions) here and there in scattered instances, until finally it finds 

 opportunity for full expression in all male Cyclorrhapha. The value 

 (if any) afforded its possessor by such a peculiar distortion is prob- 

 lematic, and it is conceivable that the males in which such an apparent 

 malformation occurs could survive despite it, if they possessed other 

 compensating advantages. On the other hand, the universal occur- 

 rence of this distortion throughout the highly successful group Cy- 

 clorrhapha, and the occurrence of a permanent rotation in many 

 other forms, together with the ability of man}^ male Diptera to twist 

 the parts about temporarily in mating, suggest that such modifications 

 may aid in the mating process, in which the participants assume the 

 diverse positions described by Hardy (1935) and Gruhl (1924), and 

 these modifications may therefore have some survival value for the 

 race. 



Recent investigators, particularly the taxonomists, are reluctant 

 to accept the view that there has been a profound torsion of the 

 terminalia in all higher Diptera, but the proofs for its occurrence are 

 very convincing to the student of comparative morphology. Males 

 of the higher Diptera furnish striking series of intergrading forms 

 illustrating various stages in the development of the distortion and 

 dislocation of the sclerites (particularly the st«rnites), and this evi- 

 dence is amply substantiated b}^ the ventral shift of the dextrai spi- 

 racles of the seventh and other segments into the ventral region (Fig. 

 12, D and H) , and is further confirmed by the distortion and displace- 

 ment of the tracheae. Still further proof of the occurrence of a tor- 

 sion of the terminalia of male Cyclorrhapha is furnished by the loop- 

 ing up of the ejaculatory duct, etc., from left to right (as the disloca- 

 tion of the sclerites indicates must have occurred) over the top of the 

 hindgut in all male Cyclorrhapha thus far studied (see Fig. 9a, A, and 

 Fig. 14, H), and the torsion of the parts has been seen to occur in the 

 pupal stage of Calliphora, by Schraeder (192'7), although he did not 

 realize all of its implications, or interpret the dislocated sternites 

 correctly.* 



The Terminalia of Male Netnatocera. In some male Nematocera, 

 such as the Tipulidae, the eighth segment may be differentiated from 

 the preceding ones in size or shape, or in the character of the processes, 

 tufts of hair, etc., that it bears, and in such cases the eighth segment 

 is considered as one of the genital segments of the male hypopygium. 

 The ninth segment, however, is the one which is the most strikingly 

 modified, and its parts furnish the characters of tlie greatest tax- 

 onomic value. 



The ninth sternite (hypandrium) is well developed in such Nem- 

 atocera as the Trichoceridae, limnobiine Tipulidae, etc., but \w most 



* It Is difficult to explain the lack of visible evidence of distorsion in the longi- 

 tudinal intersegrmental muscles of Calliphoi-a, unless certain muscles form anew after 

 the torsion, and those connecting- the tergites (which do not shift when the sternites 

 do) would naturally remain unaffected by the torsion. 



