IV.] THE COMMON SNAIL. 30I 



transfer in toto to a glass slide. Cover and ex- 

 amine in water under a low power. It appears as 

 a conspicuous round vesicle, lodging a refractive 

 black-looking granular contents. 



Examine under a high power. It is seen to 

 consist of a small sac {otocyst) closed on all sides 

 and in no way connected with the exterior. It is 

 filled with a fluid contents, in which are suspended 

 a large number of small oval calcareous corpuscles 

 or otoliths. Trace the passage of the auditory- 

 nerve into the vesicle. 



K. The reproductive elements. 



Remove a small piece of the ovotestis, and mount in 

 aqueous solution of Eosin. Examine under a low power 

 and note — 



a. The hermaphrodite follicles ; small coecal diverticula 

 of the ovotestis, from the epithelial lining of which 

 the sexual products are derived. They are arranged 

 in grape like aggregates. 



The appearances met with will be found to vary 

 with the season of the year. If spermatogenesis is 

 going on there will be found, floating in the central 

 cavity of each follicle, spermatozoa in all stages of 

 development. If the ova are undergoing maturation, 

 they will be found, in all stages, still adherent to 

 the germinal epithelium. 



Crush under the weight of a cover-glass and examine 

 under a high power. 



a. The ripe spermatozoa. Each is an elongated fili- 

 form body, bearing a small head-like enlargement 

 at one end. They are commonly met with in 

 aggregates. 



