3H 



Aaron Franklin Shiill 



the number of male-producers. Temperature, according to his 

 explanation, was only indirectly responsible for the change. He 

 further suggested that Maupas may have determined the sex of 

 the offspring by the size of the egg, which, as Nussbaum himself 

 first pointed out, is not a safe criterion. Nussbaum beheved that 

 these two explanations, together with "chance," sufficiently ac- 

 counted for Maupas's remarkable results. 



It will be profitable to state briefly the evidence which led 

 Nussbaum to the above conclusion regarding starvation. His 

 experiments are open to doubt on the ground that they were 

 not usually controlled. Possibly some experiments were controls 

 of others where it is not apparent from the text. Nussbaum rarely 

 mentions controls, hence it is probable that in most cases he did 

 not intentionally institute them. His general method seems to 

 have been to raise the rotifers under such circumstances as he 

 •could provide, watch the course of the experiments, and record 

 the changes, such as scarcity of food, gradual change of tempera- 

 ture, etc., that occurred. In certain temperature experiments, 

 however, the controls were definitely maintained. 



When an aquarium showed signs of scarcity of food and males 

 afterwards appeared in it, the experiment was taken as evidence 

 of the influence of starvation. Evidence of scarcity of food was of 

 four kinds: (a) The presence of many females in the same aquar- 

 ium, in which case there must have been less food for each one, 

 even if scarcity was not otherwise apparent; (b) a low rate of egg 

 production; (c) partial emptiness of the gut of the animals; (d) 

 direct observation of the food. There were about eighty experi- 

 ments in all. It is often difficult to decide whether starvation 

 occurred, for there were all degrees from starvation to good feed- 

 ing. I have tried to examine the published data impartially 

 with the following results. 



I. In 13 experiments many females were left in one aquarium 

 (from which it might be supposed that the food supply for each 

 was deficient), and males appeared; and in four experiments where 

 distinctly few females occupy the same aquarium, no males 

 appeared. But in at least one other experiment (54), many females 

 lived together without producing males. 



