58 CLASSIFICATION AND CREATION. 



expansion of the ventral side of the body, already 

 well developed in the Mussels and Clams. There 

 is an evident superiority in this class over the 

 preceding one, in the greater prominence of the- 

 anterior extremity,, where there are two or more 

 feelers, with which eyes more or less developed 

 are connected ; and though there is nothing that 

 can be properly called a head, yet there can be 

 no hesitation as to the distinction between the 

 front and hind ends of the bodyj 



Margarita arctica, of the coast of New England 



The third and highest class of Mollusks has 

 been called Cephalopoda, in reference again to a 

 special feature of their structure. They have 

 long arms or feelers around the head, serving as 

 organs of locomotion, by which they propel them- 

 selves through the water witli a velocity that is 

 quite extraordinary, when compared with the 

 sliuruishncss of the other Mollusks. In these 

 animals the head is distinctly marked, — being 

 separated, by a contraction or depression behind 

 it, from the rest of the body. The feelers, so 

 prominent on the anterior extremity of the Gas- 

 teropoda, are suppressed in Cephalopoda, and 

 the eyes arc conse quently brought immediately 



