OF ANIMALCULES. 



63 



some species of the Chama, and only differs from them in 

 being able to shut both ends, and alter the figure of its 

 shell, which they cannot do : this, probably, is performed 

 by means of certain articulations in the shell near its 

 extremities, which are too delicate to be discerned. When 

 these ends are open, the creature frequently thrusts out 

 at each a cylindrical fleshy part, which may be supposed 

 the head and tail, but their minuteness renders it hardly 

 possible to discover any difference between them. In 

 this posture, it is probable the creature feeds on the pro- 

 vision that surrounds it, though it depends not wholly on 

 such accidents, for it can change its place by jerks or 

 leaps, which it effects by the action of some strong 

 muscles in the two protruded parts, whose spring throws 

 it to the distance at least of its own shell's length every 

 time they are exerted. These leaps, however, have long 

 intervals between, and are never made until the animal 

 is perfectly undisturbed." 



The body, as well as the shell, is usually so transpa- 

 rent that when the latter is closed nothing can be per- 

 ceived but a slight shade within it; but occasionally I 

 have seen the body distinctly through the shell. 



" Some specimens have two or more transverse lines 

 across the body, dividing the animalcule into zones : 

 others have a couple of dark round spots ; the latter I 

 imagined to be compact ligaments, serving to open and 

 shut the shell, and similar to those that oysters, muscles, 

 he, are furnished with for the like purpose : but when 



