ORGANS OF LOCOMOTION. 27 



having seven or eight, on each side of the head ; 

 but they are less frequent in the first class, 

 though, even there, many species have two and 

 others one. How astonishing that so compli- 

 cated a structure as the eye should exist in so 

 very diminutive a creature ! 



Their organs of locomotion, or means of 

 moving through the water, are as varied as their 

 'forms. The simplest method is by the aid of a 

 proboscis, which seems to be useful both in ob- 

 taining food and in giving motion to the body, 

 the creature using it as a kind of paddle, or oar ; 

 in some species there are two of these members. 

 Others, again, have many short ones (called cilia) 

 surrounding what may be termed the mouth, 

 and by which they not only bring food to that 



