THE WHEEL ANIMALCULES (ROTATORIA) 



555 



great family of Notommatidae, and there is much reason to believe 

 that all other rotifers have been derived from forms essentially 

 similar to those found in this family. The different members of 

 the Notommatidae are so much alike that it is hardly necessary 

 to select precisely some one species for a type. But it will be well 

 in following this account to have in mind such an animal as Proales 

 (Fig. 856), or Notommata truncata (Fig. 857, A and B), or Copeus 



o 



-t 



CO. 



FIG. 856. Proales werneckii Ehr., a typical notommatoid rotifer. A, Female, dorsal view. X 400. 

 B, Male, side view. For explanation of letters, see Fig. 857. X 600. (After Rousselet.) 



pachyurus (Fig. 857, C). For convenience one can refer to any 

 member of the Notommatidae as a notommatid. 



The notommatids, though the most abundant, are as a rule the 

 least conspicuous of the rotifers. They have usually a nearly 

 cylindrical body, often somewhat swollen behind, and with a 

 slender posterior foot (/) ending in two toes (/). ' Most of them are 

 found swimming about amid vegetation or creeping over its sur- 

 face. Like all other living things, these rotifers are bundles of 

 activity. They are busily engaged in carrying on many processes, 



