Divisions of Life and Time 



ive appearance of many, even thougli it has 

 been thouglit tliat the ancestors of vertebrates 

 are to be sous^ht for in 

 this group. Here, again, 

 while every one knows 

 the class as represented 

 by such typical members 

 as the useful earthworms, 

 there are several groups 

 whose relationship with 

 creeping things is so ob- 

 scure that it long went 

 unsuspected. One of these 

 contains the Rotifera, or 

 wheel animalcules, minute 

 creatures which compara- 

 tively few have seen, al- 

 though they abound in 

 fresh water. They show 

 their relationship only in their early stages, 

 when they exhibit resemblances to the very 

 young of worms. 



Placed sometimes with the worms, some- 

 times accorded the importance of divisions of 



47 



A rotifer, a minute rela- 

 tive of the worms. Very 

 much enlarged. (From 

 Bulletin of U. S. Fish 

 Commission.) 



