Life Cycle of Hydatina Senta ^4."/ 



in the culture jars, and had probably, notwithstanding its 

 diluted state, gone on accumulating the same dissolved sub- 

 stances. This aging of the food culture is probably not sufficient 

 to account for the very large differences obtained in some of the 

 experiments; but in addition to this factor, there is the possibility 

 that the products of metabolism of the rotifers themselves have 

 the same effect as the substances derived from the food cultures. 

 These two factors may account for the result of the four experi- 

 ments in which there is a markedly higher proportion of male- 

 producers among the first-born. If, in the experiments, it be- 

 came necessary to change the water in one of the dishes shortly 

 before the end of the family, and hence to add new food, the last 

 daughter would be hatched under approximately the same condi- 

 tions as the first. In such a case the result might be like that of 

 the second part of Experiment XII, a nearly equal proportion 

 of male-producers in both first- and last-born. Unfortunately, 

 when these experiments were performed, I did not greatly sus- 

 pect the influence of dissolved substances in the water. I have 

 no notes, therefore, to show whether or not the water and food 

 were changed as I have suggested. I only know that such changes 

 were occasionally made, but do not know where. 



The conclusion that substances in the water cause the varia- 

 tion in the percentage of male-producers is quite in harmony with 

 the nearly uniform results of the experiments (VII and VIII) 

 with drainage water; and since food cultures must be frequently 

 changed, fluctuation in a long series of generations, like thatin 

 Experiment I, is probably due to the same cause. Thus practi- 

 cally the whole range of phenomena so far noted, which relate 

 to the variable proportion of male-producers may be dependent 

 on this one factor. Some of the explanations I have offered must 

 be provisional only. I am prepared to find that several factors are 

 at workinstead of one; but the simplicity of the explantion in every 

 case has led me to extend it tentatively to several phenomena 

 where its validity can be established only by further work. 



So far in this discussion, nothing has been said regarding tem- 

 perature, the factor to which Maupas attributed the most extra- 

 ordinary differences in the proportion of male-producers. Some 



