186 THE MECHANICAL FUNCTIONS. 



matter, without organization, but endowed with 

 the single attribute of voluntary motion : and 

 even this property was denied to them by some 

 authors. 



All these fanciful dreams have been dispelled 

 by the important discoveries of Ehrenberg, who 

 has recently found that even the Monas termo is 

 possessed of internal cavities for the reception 

 and the digestion of its food ; and who has ren- 

 dered it probable that their organization is 

 equally complex with that of the larger species 

 of infusoria, such as the Rotifera, in which he 

 has succeeded in distinguishing traces of a mus- 

 cular, a nervous, and even a vascular system. 



Those animalcules, whose form can be at all 

 distinguished, exhibit a great diversity of shapes, 

 and variety of modes of progressive motion. 

 Many, as the Cyclidium, have the appearance of 

 a thin oval pellicle, smoothly gliding in all di- 

 rections through the fluid : some, as the Volvox, 

 are globular ; others, as the Cercaria, are shaped 

 like a pear, tapering at one end, and often ter- 

 minating in a slender tail, so as to resemble a 

 tadpole. In many, this tail is of great length ; in 

 some, as the Furcocerca, it is forked ; in others, 

 it takes spiral turns, like a corkscrew. The 

 Kerona has processes like horns. The shape of 

 the Vibrio is cylindrical, and more or less 

 pointed at one or both ends, like an eel, or a 

 serpent, which animals it also resembles in its 



