154 FUNCTIONS AND INSTINCTS. 



have processes resembling legs. In the second 

 Class of these animals, the Rotatories, to which 

 the wheel-animalcules belong, the internal or- 

 ganization approaches to that of the higher 

 classes, for they exhibit the rudiments of a 

 nervous system ; their alimentary canal is simple ; 

 they have a branching dorsal vessel, but without 

 a systole and diastole ; their pharynx is usually 

 furnished with mandibles, which are sometimes 

 armed with teeth. The mouth of the majority, 

 especially amongst the rotatories, is fringed with 

 ray-like bristles, which Cuvier thinks are con- 

 nected w r ith their respiration. This circum- 

 stance of a circle of rays surrounding the oral 

 orifice, is found in the polypes and several other 

 animals of a higher grade. Their use in the 

 present instance, I speak more particularly of 

 the wheel-animalcules, is by their rotation to 

 produce a current in the water to the mouth of 

 the animal, bringing with it the still more minute 

 beings which constitute its food. 



These invisible inhabitants of the visible 

 world created an early interest in inquisitive 

 minds; Dr. Henry Power, and after him the 

 celebrated Hooke, about the middle of the seven- 

 teenth century, or earlier, noticed, what were 

 called vinegar eels. 1 Sir E. King, in the Phi- 

 losophical Transactions, described some experi- 



1 Vibrio Anguilla. 



