494 



THK SENSORIAL FUNCTIONS. 



to the rays of the animal, and disposed in a circle 

 round the central aperture or mouth, but occupying 

 situations intermediate between each of the rays. 

 A nerve is sent off from both sides of each ganglion, 

 and passes along the side of the rays, each ray 

 receiving a pair of these nerves. In the Holot/mria 

 and Echinus there is a similar chain of ganglia, 

 encircling the oesophagus ; and the same mode of 

 arrangement prevails in all the bivalve Molhisca, 

 except that, besides the supra-cesophageal ganglion, 



445 



448 



other ganglia are met with, in different parts of the 

 body, distributing branches to the viscera, and 

 connected with one another and with the oeso- 

 phageal ganglia by filaments, so as to form with 

 them one continuous nervous system. There is 

 one appropriated to the respiratory organs, the 

 branchial; another to the foot, the pedal; others to 

 the mouth and lips, the pharyngeal and labial; and 

 another to the mantle, the palleal ganglion. In the 

 Gasteropoda, which are furnished with a distinct 



