INTERNAL GENERATIVE ORGANS OF THE MALE. 665 



The Ejaculatory Sac and Duct (Fig. 91) differ from the parts 

 already described in having a thick cuticular intima ; this 

 often exhibits a remarkable sclerite in the wall of the ejacu- 

 latory sac, which forms the inner extremity of the ejaculatory 

 duct. 



In the Blow-fly the ejaculatory sac is ovoid in form ; it 

 measures '25 mm. in its long diameter. A remarkable fan- 

 shaped sclerite is developed in its intima. The sac consists of 

 a thick muscular coat ; the loops of muscle which surround the 

 organ and form this coat arise from, and are inserted into, 

 the sclerite. 



The vas deferens and ejaculatory duct are both connected 

 with the same pole of the ejaculatory sac, which appears to be 



FIG. 91. The ejaculatory sac of the Blow-fly, de, ductus ejaculatorius ; i/i, muscu- 

 l.ir coat covering the sac ; s, sclerite ; vd, vas deferens. 



a vesicular dilatation of the cuticular intima of the ejaculatory 

 duct. 



In many Diptera, as in Tipula, the sclerite in the wall of the 

 sac exhibits a long lever-like process, which projects into the 

 body cavity. Its strong muscular wall suggests that it acts 

 as a pump and drives the seminal fluid through the narrow 

 ejaculatory duct by its contractions. 



The Ejaculatory Duct (Fig. 91) is nearly 2 - o mm. in length, 

 and extends from the ejaculatory sac to the free extremity of 

 the penis. Its wall exhibits a muscular coat from its com- 

 mencement to the root of the penis ; its lumen measures about 

 "2 mm. in diameter. It has a thick, apparently homogeneous, 

 cuticular intima. It is very elastic and extensile. 



