120 INVERTEBRATE ZOOLOGY 



injure the nerve collar or reproductive organs. Notice that the 

 connection of the oesophagus and the salivary ducts with the 

 pharynx is near the dorsal wall of the latter organ. Observe 

 the thick muscular tongue, the organ by means of which the 

 animal grinds its food. Its surface is covered with a ribbon 

 set with small teeth, called the radula. This can be easily 

 pulled off with forceps. Mount it on a slide in water or 

 glycerine and study its surface under a high power of the 

 microscope. 



Exercise 6. Make a drawing of several of the teeth. 



The reproductive system. The snail is hermaphroditic, but is 

 not self-fertilizing. The hermaphroditic gland, which at different 

 times produces both spermatozoa and ova, is situated on the 

 inner side of the smaller lobe of the liver. The hermaphroditic 

 duct is a delicate, white, convoluted tube, which goes from the 

 hermaphroditic gland to the albuminous gland, a large white body 

 lying near the liver. From this organ the oviduct and vas 

 deferens pass forward to the genital opening near the mouth. 

 These canals are side by side and connected with each other for 

 the first part of their course, but may be distinguished by the 

 character of their walls, the oviduct having folded glandular 

 walls, while the vas deferens is a narrow tube with thin walls. 

 It is through the latter canal that spermatozoa pass out from 

 the hermaphroditic duct, while the ova pass out through the 

 oviduct, the glandular walls of which, together with the albu- 

 minous gland, secrete the albumen which surrounds them when 

 they are extruded. Near their forward end these two canals 

 separate. The oviduct loses its glandular walls, becomes cylin- 

 drical in shape, and expands to form the vagina. This is a thick- 

 walled vessel with which are connected the following accessory 

 genital organs : the receptaculum seminis, a small spherical organ, 

 already mentioned, lying in the bend of the intestine and joined 

 with the vagina by means of a long tube which lies along the 



