THE WHEEL ANIMALCULES (ROTATORIA) 



565 



other. Such a survey gives strongly the impression that the other 

 rotifers have been derived by various modifications from rotifers 

 having in general the characteristics of the Notommatidae. Space 

 will not permit setting forth in detail the grounds for this impres- 

 sion, nor will it allow describing the many forms transitional be- 

 tween the Notommatidae and other groups. But in giving an 



sp 



CO 



FIG. 863. Male of Rhinops vitrea, 

 Hudson, showing presence of 

 the alimentary canal, co, cop- 

 ulatory organ; mx, mastax; o, 

 esophagus; sp, spermarium; 

 st, stomach. X 400. (After 

 Rousselet.) 



CO 



FIG. 864. Male of Copeus pachyurus Gosse, 

 showing absence of alimentary canal, br, 

 brain; co, copulatory organ; sp, sperma- 

 rium. X 260. (After Dixon-Nuttall.) 



account of the other rotifers, they will be grouped about the No- 

 tommatidae in the way which appears to be called for by the facts. 1 



1 This follows mainly Wesenberg-Lund (1899), who has developed a classification 

 of the Rotifera based on their origin from Notommatoid forms. While this classifi- 

 cation has not thus far been commonly employed, the same can be said of any other 

 classification that has been proposed. The writer is convinced that the classification 

 given by Wesenberg-Lund is the only really natural one and that its use is a great 

 aid to an understanding of the Rotifera; he has therefore employed it. It should be 

 noted, however, that the arrangement here given differs in many details from that of 

 Wesenberg-Lund, as the advance of knowledge, or the writer's own experience, seems 

 to require. No scheme of classification can be completely fixed until knowledge of 

 the organisms to be classified is infinitely more complete than is the present knowledge 

 of the Rotifera. 



