62 HOW TO USE THE MICROSCOPE 



food to their mouths. There are several details in 

 the anatomy of Lophopus worthy of careful observa- 

 tion, and the characteristics of this species should 

 be compared with those of other polyzoa, both 

 fresh-water and marine. A low power is sufficient 

 for tliis object, and with dark-ground illumination 

 it is seen in all its glory. 



The various species of Eotifers (literally, " wheel- 

 bearers ") which are to be found in a pond, some 



Fig. 22. — Common Rotifer (Eotifee Vulgaris). 



attached to vegetation, others free-swimming, also 

 call for the student's attention. Fig. 22 represents 

 the common rotifer. Note the sucker-like foot, the 

 transparent body in which the internal organs are 

 displayed, and the two discs at the head. These 

 discs are edged with cilia or fine lashes, which wave 

 in unison in such a manner as to make it seem as if 

 the discs are rotating Uke wheels. It was this 

 appearance that led early observers to call these 



