536 THE AMERICAN NATURALIST [Vol. XLVI 



gleicbscbenkeligen Kreuzes sichtbar wird" (Daday, p. 153). Jedes 

 dieser zwei versebieden gebauten Weibcben vermag sowohl Weibchen 

 ihrer eigenen Gestalt partbenogenetisch hervorzubringen, als aueh Weib- 



Daday's work on the rotifers has in general been fre 

 quently criticized and all but discredited, and this ob- 

 servation on his part of a reciprocal relationship between 

 A. sieboldi and a saccate Asplanchna fares no better at 

 the hand of Wesenberg-Lund. He replies that he has 

 himself reared A. sieboldi in an aquarium for a month, 

 that he has studied them thoroughly and has found no 

 such reproductive phenomena. He continues, that Daday 

 has simply been mistaken in his observations, having 

 failed to distinguish the humped A. sieboldi from the 

 saccate rotifer, because the humps of the former species 

 are often retracted, giving it for the moment a saccate 

 form. 



This criticism of Daday 's reported observations may 

 of course be correct, but it seems as naive as it is severe. 

 It is of course true that the humped rotifers retract the 

 lateral humps; but the position of these protuberances 

 always remains marked by folds of the body wall, while 

 the ventral hump is not retracted at all. Daday must 

 indeed have been a poor observer to be thus deceived, the 

 more so, in that the moment these animals are placed 

 under the pressure of a cover glass or even in a very 

 shallow drop of water on a slide, the pressure of the cover 

 glass or their own weight forces them to expand the 

 humps and instantly reveal their type of structure. In 

 the light of my own study it seems far more probable that 

 Daday was correct in his reported observations than that 

 Wesenberg-Lund is correct in his criticism of them. 

 The fact that Wesenberg-Lund reared the humped 

 Asplanchna for a month without the occurrence of hetero- 

 genesis is of no especial significance. The writer has 

 reared the humped form discussed in the present paper 

 for longer periods than this with the same result. 



