ATTEMPT TO RE-CLASSIFY THE EOTIFERS. 345 



Unfortunately Ehrenberg has thrown these two families into 

 one group — the Zygotrocha, and has thus brought together 

 most widely differing forms; for the Brachionsea are highly 

 organised Rotifers^ while some of the Philodinsea are very 

 worm-like^ and the structure of the troehal disc^ jaw, and 

 foot in the two families is widely unlike. 



Of the two remaining families, I think that the Euchlani- 

 dota should be retained, though its genera require revision ; 

 but the other family, the Hydatinsea, contains such a number 

 of dissimilar creatures that nothing can save it from sub- 

 division. A glance at such a motley group as Hydatina 

 senta (fig. 1), Notommata aurita (fig. 4), Triarthra 

 longiseta (fig. 8), Synchseta mordax (fig. 3), Pedalion 

 mirum (fig. 12), and Asplanchna Brightwellii (fig. 2), 

 would be enough to make one hesitate to include them in one 

 family; and when it is found that they differ greatly in their 

 internal structure, as well as in their outward form and habits, 

 it becomes tolerably certain that this very large and hetero- 

 geneous family cannot be retained as it is. ^ 



To sum up then, we may safely say that the majority of the 

 Rotifers in the first great section, the Monotrocha, do form a 

 distinct and fairly natural group ; but that its subdivisions, the 

 Holotrocha and the Schizotrocha, cannot be maintained, 

 while its families must be altered and the genera re-arranged. 



The other great section, the Sorotrocha, must be abandoned ; 

 as containing animals that by no means resemble each other in 

 the way that those of the Monotrocha do : and its subdivisions, 

 the Poly trocha and Zy go troch a, are equally faulty; uniting 

 dissimilar families such as the Philodinaea and Brachionsea, 

 while separating similar ones, as the Brachionsea and Eu- 

 chlanidota. The families, the Philodinsea, Brachionsea, 

 and Euchlanidota, will in the main hold their ground, but 

 the Hydatinsea must be split up and rearranged. 



