i04 TAYLOR : LIFE HISTORY OF HELIX ASPERSA. 



regions. The aorta in going to the head traverses the nerve 

 ring. 



Nervous System. This consists of a nerve collar sur- 

 rounding the oesophagus. Anteriorly we have the cerebral or 

 supra-oesophagial ganglion pair, giving off a pair of nerves to 

 the buccal ganglia on the ventral surface of the buccal mass. 

 They also supply the great and small tentacles with nerves. 

 The infra-oesophagial ganglion represents the pedal, parietal 

 and visceral which are all fused into one mass. Several nerves 

 are given off from this to the foot and other parts of the body. 



Generative Organs. H. aspersa is monoecious, the 

 male and female reproductive organs being found in the same 

 individual. There is a generative gland termed the ovotestis 

 or hermaphrodite gland situated behind the liver in the smaller 

 convolutions of the shell. It develops both spermatozoa and 

 ova, but . at different periods. The ovisperm duct leaving it, 

 soon divides into a female portion which has thick glandular 

 walls and a more slender male portion or sperm-duct. A large 

 albumen gland sends its contents into the former. This division 

 into two canals is at first only partial, but lower down they 

 become completely divided. The sperm-duct opens into an 

 eversible portion or penis, to which a long fiagellum is attached, 

 while the oviduct leads to a large chamber termed the * vagina.' 

 Sperms received during copulation pass up through the genital 

 opening into the vagina, and are thence conveyed by a sperma- 

 tophore through the spermathecal duct into the spermatheca, 

 where they are stored up for future use. There is also an 

 appendix attached to the duct. Lastly we have to mention the 

 dart-sac containing a calcareous spicule known as the dart, and 

 two digitate, dilutant, or mucous glands, both opening into the 

 vagina. 



Dart-sac single, club-shaped, whitish or greyish-white at 

 all ages. Outer coat thick, tough, whitish, somewhat trans- 

 parent; inner coat whitish, vascular, or puffy. Length lo — 

 1 1 mm. To each side of the base of the sac is attached a 



J.C, iv., Oct., 1883. 



