INFUSORIA. 27 



arose in consequence of such observations ; some con- 

 tending that Monads were merely living globules with- 

 out animal organization, but capable of uniting into ani- 

 mated masses, and thus of forming the flesh and blood 

 of organized creatures. According to this doctrine, all 

 other animals, including us, human beings, are nothing 

 more than great congregations of Monads. That great 

 naturalist, Buffon, was the author of this hypothesis, and 

 therefore it is hardly necessary to say that it had many 

 profound advocates. It would neither interest nor in- 

 struct the student in physiology to give a detail of other 

 opinions concerning these living motes, since the more 

 perfect microscopes of later philosophers have shown 

 that these animals are regularly and carefully organized, 

 having not only a stomach, but such other organs as fit 

 them for their station in life. 



Wheel Animal. The Rotifera, or wheel animalcula, 

 Fig. 15. is one of the Infusoria race, though 

 larger than the monad. Fig. 15. re- 

 presents an animal of this order, mag- 

 nified 380 times its natural size. Its 

 name is derived from the apparatus 

 which it possesses for creating a cir- 

 cular current in the water. The or- 

 gans by which this effect is produced 

 are two in number, and are seen at 

 the top of the figure. They are situa- 

 ted on the head, but do not surround 

 the mouth, like the tentacula of the 

 polypi. They consist of circular disks, 

 the margins of which are fringed with 

 rows of cilia, bearing a resemblance to a crown wheel 

 in machinery. These wheels appear to be incessantly 

 revolving, and generally in one direction, giving to the 

 fluid a rotary impulse, which carries it around in a con- 

 tinual vortex. The constancy of this motion would 

 seem to indicate that it is as necessary to the life of the 

 animal as respiration is to the higher orders ; the revolu- 



What was the opinion of Buffon with respect to monads 7 What pe- 

 culiarity do the rotifera exhibit 1 Is the revolution of the wheel of the 

 rotifera real, or only apparent 1 



