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 body. 
ov 
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 with a velocity that is 
quite extraordinary, when compared with the 
sluggishness 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 are consequently brought immediately 
