Iniroducho7i to Animal Morphology. 299 



known function, seated in front of the nucleus and under the 

 anus, not far from its opening ; it is strongly ciliated, with 

 swollen borders and hair-like nerve endings. 



The ears are paired, round vesicles, usually behind 

 the eye, close to the foot ganglion, rarely to the 

 epipharyngeal (CEolidae, Abranchiata, Heteropoda). 

 They are generally in contact with the nerve centres, 

 more rarely on the end of a nerve (Heteropoda), or the 

 vesicle may have a stalk reaching to the foot ganglion 

 (Neritina, Elysia). There are often many otoliths 

 (100 in Pleurobranchia, 40 in Doris), which are some- 

 times pillar-like and arragonitic, sometimes only one 

 and lamellar, as in Martynia, Tergipes, Rhodope, or 

 mulberry-like (Phyllirhoe). In Paludina the ear sac is 

 movable by muscles. The otocyst is ciliated within, 

 but the cilia disappear in old individuals of some 

 species. The nerve sometimes enters the sac in two 

 or three filaments. A tube leads from the surface to 

 the otocyst in some Pulmonates. A sympathetic sys- 

 tem exists in the form of a pair of oesophageal gan- 

 glia joined by a commissure, with other posterior 

 visceral ganglia in pairs. 



Prosobranchs are usually dioecious : Pulmonates 

 and Opisthobranchs usually hermaphrodite. In Opis- 

 thobranchs most commonly all sex products are formed 

 in one set of follicles in a hermaphrodite gland, or 

 there may be separate male and female follicles in the 

 one gland, or separate glands in the one animal. The 

 reproductive organs are usually on the right side, in 

 the post-abdomen, seldom separate from the liver, and 

 there is a common duct widening into a uterus, with 

 w^hich communicates a gland for the secretion of the 

 nidamental capsule in which the %<g% is laid. The 



