198 



SECOND GREAT DIVISION. 



MOLLUSC A.* 



THE jointed and bony skeleton has now, as we 

 have seen, disappeared; the nervous matter, the 

 source and centre of all sensation, is no longer con- 

 centrated into a great mass at the end of a single 

 column, but scattered in knots, called ganglia, in 

 different parts of the body. One large ganglion, 

 however, situated upon the throat (oesophagus), and 

 giving out nerves to the organs of sense, undoubt- 

 edly answers to the brain of superior animals ; and 

 all the scattered masses, while giving out nerves to 

 various parts of the body, communicate with this 

 principal ganglion. 



" Various are the forms and widely different the 

 relative perfection of the Mollusca, as regards their 

 endowments and capabilities. Some, as the Bar- 

 nacles, ( Cirrhopoda,) fixed to the surface of various 

 sub-marine bodies, either immoveably or by the 

 intervention of a flexible pedicle, entirely deprived 

 of organs connected with the higher senses, and 

 unable to change their position, are content to cast 

 out at intervals their ciliated arms, and thus entrap 



* Mollis, soft. 



