238 



Records of the Indian Museum. [Vox.. XXII, 



the posterior and outer surface of the ganglion the optic nerve 

 arises and passes forwards and outwards external to the antennal 

 nerve and ends in the sensorj' epithelium of the eye. As we trace 

 this nerve backwards to the brain it can be seen to end in a quite 

 distinct rounded swelling which forms a localised prominence on 

 the external and posterior margin of the cerebral ganglion. From 

 the side of the cerebral ganglion immediately below the origin of the 

 optic nerve a small nerve arises, which can be seen to pass directly 

 downwards. This small branch, which is the nerve to the otocyst, 

 passes down external to the lateral retractor muscle of the buccal 

 mass and the pedal ganglion and finally ends in the otocyst, 

 which lies a little behind and to the outer side of the pedal nerve 



sb rv 



G-:p.7v. 



Fig. g — Vivipara bengalensis, nervous system of the left side, aiii.ii. 

 antennal nerve ; a/).?;., anterior pedal nerve ; 6. c, buccal commissure ; i.^., buccal 

 ganglion; 4. »., buccal nerve ; c./;.c., cerebropedal commissure; c.pl.c, cerebro- 

 pleural commissure ; e.pn., epipcdial nerve ; l.p v., lateral pedal nerves ; opt.n., 

 optic nerve ; ot., otocyst ; p.g., pedal ganglion ; pl.g.. pleural ganglion ; sb.ii.. sub- 

 intestinal or left parietal nerve. 



close to its origin. Each otocyst is a small oval sac, the long axis 

 of which is vertical ; it has a shining refractile appearance and its 

 cavity is filled with a number of small calcareous concretions of 

 varying shape, the otoliths. [For more detailed descriptions of this 

 organ, the reader is referred to the accounts given by Lej-dig (1850). 

 and Lacaze Duthiers (1872).] The position of the pleural ganglia and 

 consequently the arrangement of the nerve commissures that arise 

 from the cerebral ganglia differ on the two sides of the body. On 

 the left side, the pleural ganglion lies mid-way between the 

 cerebral and pedal ganglia and the arrangement of the ganglia and 

 commissures conforms to Moore's definition of the 'dystenoid' type 

 of nervous system. On this side of the body two commissures, 

 that differ markedly from each other, arise from the ventral aspect 



