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TEXT-BOOK OF ENTOMOLOGY 



While in insects there is but a single pair of genital outlets, 

 the serial arrangement of the testicular (Fig. 458) and egg-tubes 

 (Fig. 459) in some Thysanura (Campodea, Japyx, and Lepisma), 

 where the tubes' (5 to 7 on each side) open singly one behind the 

 other in segmental succession, indicates that in their ancestors these 

 egg-tubes opened out on different segments situated one behind the 

 other. Each egg-tube independently opens into one of the two 



D 



A 



FIG. 468. Male genital organs of Thysanura : A, Lepisma in which the testes are segmentally 

 arranged. After Grassi. , Lepiwna saccharina, young $ : vd, vas deferens ; ed, ejaculatory 

 duct ; ga, external appendages, After Nassonow. C, Machilis, the testis lateral and separate, but 

 not corresponding to the segments. D, Japyx, with an undivided testicular tube on each side ; 

 tt, testes ; cd, vas deferens ; , seminal vesicle ; ce, ejaculatory duct. After Grassi, from Perrier. 



oviducts, which extend through the abdomen as straight canals. 

 The two oviducts open externally by a short unpaired terminal por- 

 tion, which in Machilis is said to be wanting, only the outer aper- 

 ture of the two oviducts being in this case common to both. In 

 Campodea and in the Collembola the ovaries and testes on each side 

 are simply tubes. It is to be observed that in the young Lepisma 

 Nassonow found that the external openings of the two ejaculatory 

 ducts are paired (Fig. 458 B, ed.}. 



In the Stylopidae, also, though this may be the result of adaptation to the 

 singular parasitic hahits of the females whose bodies are mostly situated in the 

 abdomen of their host, the ends of the oviducts are formed by the invagination 



