lOO PHYLUM MOLLUSCA 



the nerve collar or reproductive organs. Notice that the connec- 

 tion of the oesophagus and the salivary ducts with the pharynx 

 is near the dorsal wall of the latter organ. Observe the thick, mus- 

 cular 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 the 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 hermaphro- 

 ditic gland to the albuminous gland, a large, white body lying near 

 the liver. From this organ the oviduct and vas deferens pass for- 

 ward 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, whereas the vas deferens 

 is a narrow tube with thin walls. It is through the latter canal 

 that spermatozoa pass out from the hermaphroditic duct ; the 

 ova pass out through the oviduct, the glandular walls of which, 

 together with the albuminous 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 cylindrical in shape, and expands to form the vagina. 

 This is a thick-walled vessel with which are connected the follow- 

 ing accessory genital organs : the receptaculum seminis, a small, 

 spherical organ, already mentioned, lying in the bend of the intes- 

 tine and joined with the vagina by means of a long tube which lies 

 along the oviduct ; the mucous glands, two bunches of tubular 

 glands; and the dart sac, a thick-walled sac which contains a 

 calcareous spicule. Identify these organs. 



The vas deferens, after separating from the oviduct, passes 

 under the retractor muscles of the tentacle to the distal end of 



