550 



THE SENSORIAL FUNCTIONS. 



ganglia, equal in number to the rays of the 

 animal, and disposed in a circle round the cen- 

 tral 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 Holo- 

 thuria there is a similar chain of ganglia, 



446 



445 



448 



encircling the oesophagus ; and the same mode 

 of arrangement prevails in all the bivalve Mol- 

 lusca, except that, besides the oesophageal ganglia, 

 others 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. In the 



