122 CLAUDE W. MITCHELL 



The one peculiar instance of the sudden change in type which 

 does not at first thought seem interpretable as due to quantita- 

 tive or quahtative nutritional change, is the tendency towards 

 mutation shown by the early generations following the resting 

 egg. But, upon second thought, this instance groups itself 

 readily with the others. The newlj^ hatched Asplanchna grows 

 first upon the stored nutrition of the egg and frequently continues 

 to develop to a point of starvation before food is taken. Thus, 

 in the first and second generations, especially if the- food organism 

 be a different one from that upon which the parent fed, we have 

 really a definite instance of changed nutrition, a change, as said, 

 which is always quantitative and may well be qualitative also. 



DISCUSSION OF LITERATURE 



In general, little experimental work has as yet been done upon 

 rotifers, in regard to their morphological characteristics, which 

 need here be considered. Beside the paper of Dr. Powers men- 

 tioned at the beginning of this article and which need not here 

 be discussed, there remains the brief series of experiments by 

 von Lange upon the very closely allied rotifer which he designates 

 A. sieboldii. Von Lange's effort was to substantiate Daday's 

 contention of dimorphisn in the rotifer, and this he was easily 

 able to do, rearing from the resting egg the saccate form, which 

 passed, during the third to the seventh generation, into a humped 

 Asplanchna. He was unable to carry his experiments beyond the 

 eighth generation. What most concerns us here is his purely 

 speculative suggestions as to the cause of the transition from the 

 saccate to the humped type. He assumes that the appearance 

 of the humps is due to an increase in vitality — ''Steigerung der 

 Vitalitat" — but, curiously enough, he attributes this increase in 

 vitality to the mere act of parthenogenesis as such, evidently 

 deeming that the development through two to six generations 

 of parthenogenesis is in itself the cause of the transition to the 

 humped type. It is obvious that such an assumption cannot 

 stand in the light of our experiments, which show that partheno- 

 genesis in and of itself possesses no inherent tendency towards 



