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 
Vic. 106.—A ventral view of the internal or anal valves of the male Blow-fly. 
a, anus; d, dorsal scale of valve; 7, internal valve; m, retractor muscle ; 
7, rectum. 
genital sternum. The organ is considerably elongated by this 
movement ; probably its length is increased by about one half. 
The Bulb (Pls. LI. and LII., 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- 
