64 D. BRYCE ON A MEW CLASSIFICATION OF THE BDELLOID ROTIFEKA. 



into two sub-classes, the Digononta (or two-ovaried), comprising 

 the Bdelloida and the Seisonidae, and the Monogononta (or one- 

 ovaried), including all other Rotifera. 



. In a useful monograph on the Philodlnaea, published in 1893, 

 Janson (38) discussed at some length the views and suggestions 

 of earlier w^riters and, in particular, those of Hudson and GossCy 

 and of Milne. On the one hand, he criticised the creation by the 

 former authors of the family of the Adinetadae. On the other, 

 he admitted the contention of Milne that under the definition of 

 Ehrenberg many eyeless species would be classed as Callidinae, 

 although in respect of their structure they should clearly be 

 regarded as belonging to the genus Rotifer. Nevertheless he 

 hesitated to accept the genera proposed by Milne, and preferred 

 for the time to abide by the Ehrenbergian family of Philodinaea, 

 which in his view covered all the various genera. He made the 

 one correction of transferring to the genus Rotifer the two species 

 which had been assigned to Actinm'ics, recent discoveries having 

 shown the differences betAveen these two genera to be less definite 

 than had previously appeared. 



In an important treatise published in 1899 Wesenberg Lund 

 (50) dealt in great detail with the wide cjuestion of the relation- 

 ship to each other of all the various groups of the Rotifera, and^ 

 in conclusion, put forward a new classification based largely upon 

 results afforded by his own investigations. At the outset he 

 followed Plate in dividing the class Rotifera into the sub-classes 

 Monogononta and Digononta according to the number of ovaries 

 possessed by each species. So far as regards the Monogononta, 

 the subsequent grouping of the families and genera was carried 

 out on principles essentially different from those of Hudson and 

 Gosse. The Digononta, on the other hand, were little affected 

 by the investigations of the author, according to whom this sub- 

 class included the two orders Bdelloida and Seisonacea, the latter 

 created to receive the family of the Seisonidae. While accepting 

 from Hudson the order of the Bdelloida, Wesenberg Lund 

 followed Janson in placing all the Bdelloid genera in one family, 

 J^hilodinidae, and in rejecting the genus Actinurus. The family 

 Thilodinidae of W^esenberg Lund would thus be equivalent to 

 Ehrenberg's family rhilodinaea, and according to the author 

 included the five genera Rotifer, Rhilodina, CaUidina, Discopus, 

 and Adineta. 



