236 Records of the Indian Museum. [Vol. XXII, 



acetic acid and are presumably calcareous in nature. It is prob- 

 ably from these spicules that the young embryo derives the 

 calcareous substance necessary for the production of the shell. 



-^ The Nervous System. 



A very full and complete account of the nervous system of 

 Vivipara vivifara has been given by Bouvier (1887, pp. 63-72 , pi. iv, 

 figs. 15, 16) and that of Vivipara bcngalensis agrees in almost every 

 particular, so far as I have been able to ascertain. The type of 

 nervous system is that known as ' dial3'neurous,' in that the 

 connection between the sub -intestinal nerve and the right pleural 

 or parietal ganglion is an indirect one, brought about bj' the union 

 of a branch arising from the right pallial nerve and a branch 

 from the sub-intestinal nerve. A similar anastomosis exists on 

 the left side of the body, between the left pallial nerve and a 

 branch from the supra-intestinal ganglion. Moore (1903, p. 276) 

 has distinguished three different types of nervous system, based 

 on the relative positions of the three main ganglia of the central 

 nervous system — those forms of nervous system in which, as in 

 Vivipara, "the pleural ganglia are more or less h:^.lf-way between 

 the cerebrals above and the pedals below the oesophagus" he 

 terms ' dystenoid.' 



The cerebral ganglia are situated in the base of the snout on 

 either side of the commencement of the oesophagus, immediately 

 behind the buccal mass. Each ganglion is roughly triangular in 

 shape, with the base posteriorly and the apex pointing forwards 

 and outwards. On the external aspect a shallow groove divides 

 the ganglion into two parts, an anterior ' labial ' portion and a 

 posterior ' cerebral ' portion. Each ganglion is of a red-brown 

 colour and is connected with its fellow across the dorsal aspect of the 

 oesophagus by a wide, short cerebral commissure. The ducts of the 

 the salivary glands pass forwards close to the middle beneath this 

 commissure and above the oesophagus. The ' labial ' portion of 

 the cerebral ganglion is flattened dorso-ventrally and from its 

 outer and antero-intenial borders a number of nerves arise. From 

 the antero-internal border two fine nerves arise close together and 

 pass forwards over the dorsum of the buccal mass to the skin of 

 the snout. Near the apex of the ganglion, but still from the inner 

 border, a stout nerve arises and passes forwards on the side of the 

 buccal mass to the snout and lips. At the extreme apex of the 

 ganglion three nerves arise close together : (i) this runs forwards 

 on the side of the buccal mass to the lips and snout; (ii) this is 

 the stoutest of all three and is the buccal nerve. It first passes 

 downwards and forwards on the lateral aspect of the buccal mass 

 towards the ventral aspect : here it turns upwards and passes deep 

 to the lateral retractor muscle of the lips, and just above and 

 behind the origin of this muscle from the side of the odontophoral 

 cartilage it ends in a rounded or triangular yellowish-brown body, 

 the buccal ganglion, which lies just in front of and below the 

 point of entrance of the salivary duct into the buccal cavity_ 



