STRUCTURE OF WHEEL- ANIMALCULE. 321 



subject to the will of the animal. When satisfied with the sup- 

 ply of food it has obtained, the movement of its wheels no longer 

 continues ; and the lateral projections on which they are situated 

 then usually fold themselves inwards, so as to conceal them. 

 The form of the animal the head still projecting then closely 

 resembles that of a Leech ; and the movements which the Rotifer 

 performs in this condition, are by no means unlike those of that 

 animal. Sometimes it detaches itself altogether, and swims 

 freely through the fluid, as if in search of a new pasture. In 

 other instances it attaches itself by the head, which is furnished 

 with a sort of sucker for the purpose ; and then, by shortening 

 the body, draws up the tail into close proximity with it. It 

 then attaches the tail, and, detaching the head, extends the body 

 so as to project the head to a considerable distance, where it 

 takes a new hold of the surface upon which it thus creeps. The 

 rapidity and precision with which these movements are executed, 

 display a considerable amount of muscular energy on the part 

 of the animal, as well as of that capability of adapting its opera- 

 tions to circumstances, which indicates sensations of some acute- 

 ness. When the body is elongated to its full extent, the intestinal 

 canal runs nearly straight ; and the eggs, which may usually be 

 seen by its side, lie apart from one another. But, when the body 

 is contracted, the alimentary tube becomes serpentine, and the 

 eggs by its side, appear to be in close contact. The great amount 

 of muscular contractility, and the flexibility of the integument in 

 this animal, enable it thus to contract itself more than most of 

 its class. It is not unfrequently seen to assume quite a globular 

 form ; and this is its usual aspect when it dies, or when the water 

 evaporates. The reproduction of the Rotifer is not accomplished 

 by spontaneous subdivision, or by the production of buds, such 

 as we shall see to occur in the lower Infusoria ; it takes place 

 only by eggs, in the manner already mentioned. Although not 

 many eggs are produced at once, yet these so speedily become 

 capable of producing others in their turn, that the multiplication 

 of these beings takes place with extraordinary rapidity. A cal- 

 culation, made by Ehrenberg, from data furnished by experiments 

 upon another species, will be presently given ( 861). 





