THE EXTERNAL GENERATIVE ORGANS. 



743 



The Great Apodemes. The whole penis is supported by two 

 great apodemes, which are united in the middle line. They 

 articulate with the saddle of the paraphalli and receive the 

 insertion of a large mass of muscles, which arise partly from 

 the genital sternum and partly from the terga of the genital 

 somites. The action of these muscles is to rotate the penis from 

 its position of rest, and to render tense the loose syndesmosis 

 by which the saddle of the paraphalli is articulated with the 



i 



FIG. 106. A ventral view of the internal or anal valves of the male Blow-fly. 

 a, anus ; d, dorsal scale of valve ; /, internal valve ; m, retractor muscle ; 

 r, rectum. 



genital sternum. The organ is considerably elongated by this 

 movement ; probably its length is increased by about one half. 



The Bulb (Pis. LI. and LIL, b). Two chitinous plates on 

 the upper aspect of the root of the penis, behind the ventral 

 processes of the paraphalli, form a bulbous enlargement at the 

 base of the organ. This bulb is notched in front, so that it 

 exhibits two rounded lobes. 



The Meso- and Meta-genital Somites. These somites are un- 



