APLYSIA. 241 



ctenidium so as to obtain as much oxygen as possible. If 

 foul water enters, the parapodia are forcibly closed and the 

 ctenidium withdrawn. 



The osphradium consists of a slightly elevated patch of 

 columnar epithelial cells. These are not ciliated, and the 

 organ shows no trace of the leaf-like arrangement of the 

 osphradium of certain Prosobranchs (e.g., Buccinum). The 

 osphradium is innervated from the branchial ganglion. 



GENERATIVE SYSTEM. 



(Figs. 18-20.) 



Aplysia, like other Euthyneurous Gastropods, is herma- 

 phrodite. The genital organs consist of an unpaired ovotestis 

 or hermaphrodite gland, a common genital duct, female 

 accessory glands, reservoirs for the male elements, and a male 

 copulatory organ or penis. 



The ovotestis (Fig. 20, herm. gl.) is a compact gland of 

 irregular shape, and is embedded in the visceral mass on its 

 right posterior border. In the freshly-killed animal it can be 

 easily separated from the liver, and its golden yellow colour 

 forms a marked contrast to the dull brown of the latter. 

 A common genital duct forms a mid-rib to the gland, and 

 receives ductules from both sides. The size of the gland 

 varies with the time of year and age of the specimen. On 

 leaving the ovotestis the little hermaphrodite duct (lit. herm. d.) 

 increases in width and becomes sinuous. It separates itself 

 from the visceral mass and passes forward to the right of the 

 latter beneath the floor of the pallial cavity. It is held in place 

 by enveloping connective tissue, which fastens it to the right 

 body wall. At the level of the anus an ovoid mass, consisting 

 of -the female accessory glands and a reservoir for sperms, 

 occurs on the left of the duct. These accessory glands are 

 small and poorly developed in young specimens, and only 

 become fully developed when the animal is sexually mature. 



