NO. 14 



INSECT ABDOMEN SNODGRASS 



17 



ducts with separate orifices. The two penes are supported either on a 

 pair of divergent basal arms (B, C, D, E, ;r), or on a common basal 

 plate (F, K, x) with lateral prolongations. The ends of the basal arms 

 are always intercalated between the adjacent lower angles of the 

 tergal plates of the ninth and tenth abdominal segments {B, x, x'), 

 in some forms they are more closely attached to the ninth tergum, 

 in others to the tenth. The supporting structure of the penes is usu- 

 ally concealed above the styliger plate, and is implanted on a mem- 



^Sty 



Fig. 26. — Ephemeroptera : copulation and external male genitalia of Cinygmula 

 mimus. 



A, male and female in copulation (drawn from a slide mount loaned by Dr. J. G. 

 Needham). In life probably the body of the female is more nearly parallel 

 with that of the male, and her thorax held in the loop of the long front tarsi of 

 the male. B, the copulating parts of same, more enlarged, showing the use of 

 the styli as claspers. C, end of male abdomen, ventral view. 



Ccr, cerci ; Cxpd, coxopodite plate, or styliger ; Pen, penis ; Sty, stylus. 



branous area or fold between the ninth sternum in front and the 

 paraprocts behind (B). There is thus no part of the venter of the 

 male abdomen that can be referred to the tenth segment unless it is 

 the basal plate or arms of the penes and the supporting membrane. 

 Considering the evidence (see page 58) that the primary gonoducts 

 of male insects opened on the tenth abdominal segment, it is consis- 

 tent to suppose that the primitive paired penes were processes of the 

 sternum or of the appendage bases of this segment. The paired 

 penes of the Ephemeroptera, being evidently primitive organs, should 

 therefore belong to the tenth abdominal segment, and the forward 



