24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 09 



When the vaginal opening Hes behind the ninth sternum it may come 

 into juxtaposition with the anal opening, particularly when the ter- 

 minal segments of the abdomen are reduced or partly suppressed, and 

 in some cases, as in Lepidoptera and certain Trichoptera, the vagina 

 and rectum open together into an ectodermal depression, or cloaca, 

 which constitutes the extreme posterior extension of the median egg 

 passage. 



The position of the functional female genital opening of pterygote 

 insects is now seen to be so variable in different orders, and even 

 within a single order (Hemiptera, Lepidoptera, Trichoptera, Diptera), 

 that it can be given little value as a character for determining the 

 relative positions of groups in classification. Thus, as shown by 

 Busck (1931) in the Lepidoptera, several of the more generalized 

 families in both the Jugatae and the Frenatae have only the posterior 

 opening on the ninth segment, while all the otherwise more specialized 

 families retain the anterior opening on the eighth segment together 

 with an opening on the ninth. 



The genital openings of Collembola and Protura. — The unusual 

 positions of the genital openings in Collembola and Protura produce 

 conditions in these groups which are different from those in any of 

 the other Hexapoda. 



The abdomen of Collembola contains not more than six segments, 

 and the median gonopore, in both the male and the female, is situated 

 on the posterior part of the fifth segment, or between this segment 

 and the sixth. The Collembola, therefore, in this respect, present 

 either a condition having no relation to that in the other insects, or 

 one produced secondarily by specialization. If we assume that the 

 small number of segments in the collembolan abdomen is the result 

 of a suppression of segments in both the pregenital and postgenital 

 regions, the problem of the position of the genital opening presents 

 no special difficulties. On the other hand, if the six segments of the 

 abdomen represent the maximum abdominal segmentation ever at- 

 tained in this group, then the common genital opening may be a 

 primitive subterminal aperture. But again, if the Collembola are de- 

 scended from insects having the usual number of somites in the 

 abdomen, and the posterior segments have been suppressed, then 

 we must assume that the genital apertures have undergone an anterior 

 migration. The general structure of the Collembola suggests a high 

 degree of specialization on a low plane of insect organization. 



The Protura present a different kind of problem, relative to the 

 genital openings, from that presented by the Collembola, for here the 

 gonopores, situated in both sexes between the eleventh and twelfth 



