Class 2. Gastropoda. 



299 



and the sperm duct opens only at the apex of the penis, which 

 cannot be withdrawn by invagination, as in other Gastropoda. 

 Glandular appendages of the sexual organs are usually wanting in 

 the Prosobranchiata. The Opisthobranchiata and Pulmo- 

 nata are hermaphrodite, and ova and spermatozoa are 

 formed in one and the same organ, the hermaphrodite 



Pig.215. Female Peri- 

 winkle (Littorina) dis- 

 sected as Fig. 241 ; some 

 portions of the body-wall 

 and some of the organs 

 (kidney, pericardium), are 

 also opened, a anus, ge 

 genital pore, h ventricle, 

 ma stomach, n kidney, 

 od oviduct, ov ovary, sd 

 salivary gland, sp oeso- 

 phagus, V auricle, z spirally 

 coiled radula sac. — After 

 Souleyet, modified. 



gland. 1'he duct is in some of the Opisthobranchs common to 

 both ova and spermatozoa, and then a common genital aperture is 

 present ; from this a groove runs along the skin to the apex of 

 the copulatory organ. In most Opisthobranchiata and in the 

 Pulmonata the duct is common only to a certain extent, for it 

 splits a short distance from the hermaphrodite gland into two 

 canals, an oviduct and a vas deferens, which usually open 

 close together, the vas deferens at the apex of the penis, which 

 is here furnished with an actual canal, not simply with a 

 groove. The penis can be invaginated in all Pulmonates and 

 Opisthobranchs. In these groups, especially in the air-breathing 



