210 22 



a segmentation in the organisation, which on one side cannot be quite overlooked, 

 but upon which, on the other side, not too much stress must be laid. 



It now will be understood tlaat I regard the soft indistinctly segmented cuticula 

 as more primitive than an unsegmented lorica, the ventral ciliary disc as the primary 

 wheel-organ from which the wheel-organ with two ciliarj' wreaths has been developed, 

 the foot which is not sharply defined from the remaining body and provided with 

 two toes as the most primitive footform of the Rotifera; further that I regard the 

 dorsal organ as developed from coalescence of two originally separated lateral organs. 

 As I further call attention to the fact that the great reduction in the structure of 

 the males is most feebly pronounced in the Notommaticlœ, it will be understood that 

 I regard this family, in which all the above-named primitive body structures are 

 more or less distinctly developed, as the most primitive of all the families of the 

 Rotifera. A closer study will show that just this family possesses the developmental 

 possibilities of the plurality of the other families, and that remarkably many of the 

 Rotifer-families, through more or less conspicuous transitional stages, seem more 

 connected with this family than with each other mutually. It seems as if most of 

 the other families of Rotifera maj' be arranged in a series of parallel developmental 

 lines, all deriving fi-om the Notommatidœ ; some of the lines may be drawn with 

 almost full certainty; with others this is not the case; some, showing no connection 

 at all, seem to be totally aberrant forms. 



In my opinion the Rotifera were originally creeping organisms, bound to the 

 bottom and the vegetation. Secondarily in different ways their organisation has 

 been altered in such a wa3% that from creeping organisms they have been changed 

 into freeswimming creatures, more or less independent of the substratum, in the aber- 

 rant forms true plancton organisms. These processes of modification by means of 

 which it is only possible to understand many of the most peculiar body-structures, 

 (the connection between distinct types of mouthparts and of the wheel-organ, the 

 structure of the foot, the development of the lorica, the loss of segmentation, the 

 peculiar balloon shape, manifesting itself in verj' different genera {Asplanchna, Syn- 

 chceta, Notops {N. pelagicus Jennings) have begun not from a single but from different 

 Notommatidœ, the results of which are series of different developmental lines running pa- 

 rallel. The Notommatidœ, themselves, are almost all creeping or very slowly swimming 

 organisms. Only one plancton organism {Proalidies de Beauchamp 1917 p. 148) is known. 



In 1899, when this view was published, even if some of the main points had 

 already been observed by previous authors (Metchnikow 1866 p. 354; Joliet 1883 

 p. 204) the system, set forth by Hudson'-Gosse (Vol II p. 14), was the dominating 

 one. Upon all essential points their views differed totally from mine. According to 

 them the Notommatidœ were the most highly developed family of all the Rotifera ; 

 the tj'pical wheel-organ was two ciliary wreaths (cingalum and trochus). Great stress 

 was laid upon the fact whether a lorica was present or not. Characters deriving 

 from homogeneous life conditions were used as characters which connected families 

 together in the same order, and which had no affinities at all. The old interpréta- 



