r6tifers. 213 



CHAPTER VIII. 



RdTIFERS. 



When these transparent microscopic animals are 

 swimming or taking food, there is usually an appear- 

 ance of two, small, rapidly rotating wheels on the 

 front border of the body, an appearance that sug- 

 gested the name of Rotifera, or Wheel-bearers, for 

 the group. The two organs certainly do seem like 

 rapidly revolving wheels when viewed under a low pow- 

 er, but they are in reality two disks or lobes bearing 

 marginal wreaths of fine cilia, which vibrate so quickly 

 that the eye can usually perceive the effect only. It 

 is by the action of these cilia that the Rotifer swims 

 and captures food, the currents produced by them, 

 when the Einimal is at rest, setting in towards the 

 mouth, which is often situated between the ciliary (or 

 cilia-bearing) disks, and carrying particles of food 

 which the Rotifer accepts or rejects. As a rule the 

 ciliary disks are two separate organs, but they may be 

 united into one, or the Rotifer may have the front 

 margin of the body bordered by a single series of cilia, 

 or the disks may be entirely absent and replaced by 

 long, ciliated arms, as in Stephandceros, or by clusters 

 of long, fine hairs as in Flosculdria, both of which are 

 Rotifers. 



