192 Life Cycle of Hydatina Scnta [Dec. 



From the purely biological Standpoint, considerable interest 

 attaches to these results, because of the possible explanation they 

 give of the conflicting results of earher workers, At least some 

 of the chemical substances tested in the experiments are to be found 

 in the food-cultures from which the animals are fed. If an attempt 

 is made to starve the rotifers, a smaller quantity of the chemical 

 substances, as well as a smaller quantity of food, is admin- 

 istered. Since the effect of these substances is to reduce the Pro- 

 portion of male-producers, the supposed starvation (diminution 

 in the amount of certain substances) should increase that propor- 

 tion. Experiment shows that it does. It is not improbable, there- 

 fore, that effects attributed to diminished nutrition may really be due 

 to decreased quantities of chemical substances. 



From the Standpoint of both chemistry and biology, a very im- 

 portant question remains unanswered. It is not known how the 

 substances effect the reduction of the proportion of male-producers. 

 In general, two methods are conceivable. It seems now almost 

 certain, from other experiments, that once an tgg is laid the nature 

 of the female hatching from it can not be changed by subjecting the 

 egg or the resulting individual to manure Solution. The chemical 

 substances in Solution, therefore, may alter certain fundamental 

 processes in a given G.gg or oogonium, during growth and matura- 

 tion or at some other period, so that the individual resulting from 

 that tgg becomes a female-producer, whereas in the absence of 

 those substances the same egg might have given rise to a male-pro- 

 ducer. On the other band, the eggs or oogonia may be differen- 

 tiated into two classes by a process in nowise dependent upon the 

 chemical nature of the medium ; if this be true, the substances that 

 affect the cycle may be more toxic to one class of eggs than to the 

 other, and prevent many of the former class from being laid. 

 Experiments are now in progress which bid fair to determine which 

 of these hypotheses is correct, but the conclusions to be drawn from 

 them can not be predicted. 



Valuable suggestions were received during the progress of this 

 work from Prof. William J. Gies and Prof. T. H. Morgan. 



