48 



SOME ASPECTS OF MORPHOLOGY 



that segment or within a genital cavity or pocket which surrounds 

 the gonopore. In either case, the lobes in question ultimately 

 fuse to form the penis. This relatively simple condition has 

 been described by Metcalfe (1932a) in Gastroidea and Anihonomus 

 among Coleoptera and by Mehta (1933) in Pieris and some other 

 Lepidoptera. In other cases these lobes undergo subdivision, 

 thus giving rise to a pair of outer components or parameres and an 

 inner pair which unite to form the penis. This condition has been 



Fig. 30. Penis (p) and parameres (pa) of A, Pedetonius palcearcticus 

 Silv. (Machilidae). (After Silvestri.) B, Nicoletia wheeleri Silv. 

 (Lepismidae). (After Silvestri.) C, Ephemeroptera (Callibcetis). 

 (After Walker.) D, Dermaptera (Anisolabis). (After Walker.) 

 (c, coxite ; s, stylus ; st, ninth sternum.) 



shown to obtain in certain Coleoptera (Singh Pruthi, 1924 ; 

 Metcalfe, 1932a). Earlier observers have also described the same 

 state of affairs in some Lepidoptera as well as in Orthoptera, 

 Hymenoptera and Diptera. It is generally accepted that the 

 penis was originally a paired organ, and this generalised state of 

 affairs is retained among Ephemeroptera (Fig. 30, C) and 

 Dermaptera (Fig. 30, D). Among generalised members of the 

 last-mentioned order the parameres, however, instead of being 

 free, have become mere outgrowths of the penes. In the Thysanura 



