NERVOUS SYSTEM OF BUCCINUM. 



547 



greater concentration, and the brain exhibits much larger dimensions as 

 compared with the size of the body. Thus, in the Snail (fig. 265) we 

 find only two great nervous masses the brain (I) (a large ganglion 

 placed above the oesophagus, and supplying the nerves connected with 

 sensation), and an equally large suboesophageal mass (m), whence 

 proceed nerves to all the viscera and locomotive organs. Here, there- 

 fore, we have another example of the great law that we have already so 

 often illustrated the diminution in number and the increase in size of 

 the nervous centres as we rise from lower to more exalted types of 

 animal organization. 



Fig. 275. 



Anatomy of Buccinitm. 



(1461.) The tentacula (fig. 275, //) in the marine Gasteropoda are 

 generally not retractile, and the eyes are frequently situated at the 

 outer side of the base of each tentacle, instead of at their apex as in the 

 figure referred to ; but, with these exceptions, we can add nothing to 

 what has been said concerning the senses of these Mollusca in the de- 



2N2 



