582 TEE ROTIFERS. 



earned on with as much ease as if the skin were of crystal. Their development is wonderfully 

 rapid ; for although but a few eggs are produced at one time, they are so quickly hatched, 

 and the animal is so rapid in its growth, that Professor Ehrenberg calculated that in the genus 

 Hydatica, although only three or four eggs are produced at a time, a single individual will be 

 the progenitrix of nearly seventeen million descendants within the space of twenty-four days. 



In this class the arrangement is very perplexing to systematic naturalists, and nothing is 

 as yet settled about it. 



These remarkable beings are mostly found in water that has become stagnant, but is 

 partially purified by the presence of the Infusorians, which always swarm in such localities. 

 There is, however, one very strange residence of the common Rotifer, namely, within the leaf- 

 cells of the common bog-moss (Sphagnum). These cells are very large in proportion to the 

 size of the leaf, are kept open by spiral threads coiled in their interior, and their walls are 

 pierced with large apertures, so as to form a general communication throughout the whole 

 mass of cells. Within these curious chambers the Rotifer is found, and is able to pass freely 

 from one cell to another. They probably gain their admission in the egg state, and find suffi- 

 cient moisture in the cells for their seeds. 



The typical genus of this class is known by the name of Rotifer. In all the members of 

 this genus the body is rather elongated, and furnished at the hinder end with a kind of tele- 

 scopic tail, by means of which they can attach themselves at will to any object, and release 

 themselves whenever they please. Sometimes they move their bodies gently about, while still 

 grasping by the extremity of tail ; sometimes they are nearly motionless, while they frequently 

 rock themselves backwards and forwards so violently that they seem almost to be testing the 

 strength of their hold. 



These creatures can both swim and crawl, the former act of locomotion being achieved by 

 the movement of the cilia, and the latter by creeping along after the fashion of the leech, the 

 head and tail taking alternate hold of the object on which they are crawling. 



The masticating apparatus is always conspicuous, whether the animal have the wheel 

 protruded or withdrawn. It is situated behind the bases of the wheel-lobes, and looks, when 

 the animal is at rest, something like a circular buckler, with a cross composed of double lines 

 drawn over its surface. Even in the very young and undeveloped animals which are seen 

 within the body of the parent, these jaws form the most conspicuous portions of their struc- 

 ture, and enable them to be recognized long before they are able to go out into their watery 

 world and shift for themselves. 



All the Rotifers have a marvellous fund of vitality, and survive under circumstances 

 where animals less tenacious of life would die a thousand deaths. They have been thoroughly 

 dried by means of chemical acid, wetted and restored to life, dried again, wetted again, and 

 subjected to this treatment through many successive alternations, without perishing. 



At first sight, this animal bears a strong resemblance to several of the Molluskoids ; but 

 a closer examination shows that the apparent tentacles are nothing more than extensions 

 of the lobes on which the cilia are set, and the apparent cell is no cell at all, but a gelatinous 

 secretion from the body. In one genus, however, a veritable tube is built up, composed of 

 particles of solid matter, formed into little pellets by a special organ, and then deposited upon 

 the edge of the tube. The organ which forms these pellets is set towards the front of the 

 head, and on its under side, and looks like a little revolving disc. 



