346 0. T. HUDSON. 



Leydig's Classification. 



Leydig based his classification on the Rotifer's external form, 

 and on the presence or absence of the foot, as well as on the 

 foot's shape and length. As he quite disregarded the whole of 

 the internal structure, as well as that of the trochal disc, it is not 

 to be wondered at that his arrangement is a bad one. The first 

 of these three primary divisions brings together, on account of 

 their shape, such dissimilar creatures as Melicerta (fig. 9), 

 Dinocharis, Synchseta (fig. 3), and Philodina (fig. 13) — 

 animals differing alike in habits and internal structure, and only 

 faintly resembling each other in shape. His second primary 

 division, instead of containing any of the great natural groups, 

 simply picks out a few species on account of their sac-like shape, 

 and throws together Notommata clavulata, Polyarthra 

 platyptera,Diglena lacustris, and Asplanchna Bright- 

 well ii. Rotifers that have hardly one feature in common. 

 His third primary division, containing the Brachiontea and 

 Euchlanidota is a reasonable one enough; and of his eleven 

 families four are natural, but the rest are so unsuccessful that 

 I propose to pass over his attempt without further comment, 

 while at the same time fully admitting the great value of his 

 observations and researches. It would be doing Leydig the^ 

 greatest injustice to judge of the rest of his work from his 

 classification of the animals that he so successfully studied. 



Dujardin's Classification. 



Of Dujardin I must speak in very different terms. His book 

 is mainly critical ; and, so far as I can find, contains little on 

 the Rotifers that was new, except his observations onAlbertia 

 and Lindia. 



His criticisms are shrewd, and often just; he points out 

 that Ehrenberg^s respiratory tube is probably an antenna, and 

 suggests that the convoluted tubes with their flickering tags 

 and contractile vesicle are a respiratory system; an erroneous 



