KEPEODUCTIVE SYSTEM. 125 



opens to the exterior at the genital pore, through 

 which it can be protruded. 



To the penis is attached the retractor penis 

 muscle, a narrow muscular band, which arises 

 from the floor of the mantle-cavity, and runs 

 downwards and forwards to its insertion. 



6. The female duct and its accessory organs. 



a. The oviduct is a short thick-walled tube, running 



forwards from the point at which it leaves the 

 vas deferens. 



b. The vagina is a thick-walled tube into which the 



oviduct opens in front, and which runs forwards 

 to open with the penis at the common genital 

 pore. 



c. The mucous glands are two tufts of tubular glands, 



opening by a pair of apertures into the vagina : 

 each tuft consists of thirty to forty finger-like 

 processes. 



d. The dart sac is a large pyriform sac opening into 



the vagina just beyond the mucous glands. It 

 has very thick walls, and contains a quadrangular 

 calcareous spicule. 



e. The spermotheea, or receptaculum seminis, is a long 



ctecal diverticulum from the hinder end of the 

 vagina. It lies alongside the common duct, and 

 its hinder end is expanded into a globular dilata- 

 tion just behind the pericardium and kidney. It 

 is of about the same length as the flagellum, and 

 serves to lodge the spermatophore received from 

 another snail. 



A small diverticulum is very commonly given 

 off about a third of its length from the vagina. 

 In H. aspersa this is largely developed and forms 

 the longer portion of the spermotheea. 



Care must be taken not to mistake the spermo- 

 theea for the vas deferens, nor to cut away its 



