138 THE MECHANICAL FUNCTIONS. 



atoms of organic bodies. During the greater part of the last 

 century, infusory animalcules were the subject of frequent 

 and laborious microscopical research, and gave rise to end- 

 less conjecture and speculation as to their origin, their vi- 

 tality, and their functions in the economy of nature. Not- 

 withstanding their minuteness, considerable differences of 

 organization were perceived to exist among them: but many 

 naturalists still clung to the idea that monads, the most di- 

 minutive of the tribe, and whose very presence can be de- 

 tected only by the application of the highest magnifying 

 powers, are homogeneous globules of living matter, without 

 organization, but endowed with the single attribute of vo- 

 luntary motion: and even this property was denied to them 

 by some authors. 



AH these fanciful dreams have been dispelled by the im- 

 portant discoveries of Ehrenberg, who has recently found 

 that even the Monas terrno is possessed of internal cavities 

 for the reception and the digestion of its food; and who has 

 rendered it probable that their organization is equally com- 

 plex with that of the larger species of infusoria, such as the 

 Rotifera, in which he has succeeded in distinguishing traces 

 of a muscular, 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 ap- 

 pearance of a thin 6val 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 terminating in a slender tail, so as to re- 

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

 some, as the Furcocerca, it is forked; in others, it takes spi- 

 ral 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 undulatory mode of 

 swimming.* Some, as the Gonium, have an angular, others, 



* Animalcules refen-ible to this genus are met with in great numbers in 

 blighted wheat, (Fig. 2, p. 58,) in sour paste, and in vinegar which has lost 



