73 



following: — The Visceral nerve (fig. 41, vise.) passes 

 close to the left side of the vas deferens in the male and 

 innervates the digestive gland and gonad. It is an 

 extremely long nerve, in fact, the longest in the animal, 

 and can be traced to the tip of the visceral mass. Two 

 nerves, the recto-genital and rectal, (fig. 41, rec.' and 

 rec.) pass out to the right, to the rectum and gonoducts. 

 A larger nerve, the reno-cardiac (fig. 41, r.c.) passes out, 

 breaking up very considerably on its way and sending a 

 branch to the pericardium and heart. Erom the smaller 

 ganglion a nerve arises which passes to the efferent 

 branchial vessel (fig. 41, eff.). 



THE SENSE OKGANS. 



The sense organs may be divided into simple and 

 compound, the former class including only the numerous 

 sense cells which occur scattered amongst the ordinary 

 epithelial cells, the latter the Eyes, Osphradium, and 

 Otocysts. 



The Eye. 



The eyes are two in number and are situated at the 

 base of the tentacles, on the dorsal surface of a small 

 lateral protuberance. 



They are visible as two round intense black spots, 

 but when the tentacle is contracted and the body wall is 

 thrown into folds, the eye, hidden in the angle between 

 tentacles and head, is not easily seen. No metallic 

 glitter so characteristic of the Pecten eye ever occurs, 

 and, as will be seen below, the layer in the eye responsible 

 for this feature is not present. 



The lowest gastropoda possess eyes which are simply 

 sac-like invaginations of the outer epithelium. At the 

 bottom of the sac the epithelium is modified somewhat 



