MALE-PRODUCTION IN HYDATINA 



137 



more concentrated solutions of which were known to have the reverse 

 effect. Among the substances tested were the three named above. 

 Since all of them reduced male-production or showed no effect, the 

 results of the several experiments are for brevity suimnarized in a 

 single table (table 8). 



TABLE 8 



Summaries of several experiments with dilute solutions of potassium sulphate, iron 

 chloride, and ammonium chloride. The number of male-producers is not increased 

 by any of these substances, but in most cases is reduced 



FACTORS SUGGESTED BY WHITNEY S EXPERIMENTS 



Whitney ('14) reared Hydatina on a diet of ChlamydomonaS) 

 and obtained a striking increase in the proportion of male-pro- 

 ducers. He freely attributed this effect to the (qualitative) 

 difference in nutrition, mthout mentioning several agents whose 

 possible effects had not been eliminated. For example, his food 

 cultures were started in different media; Chlamydomonas was 

 reared in a solution of bouillon cubes, the Polytoma used in the 

 control was reared in manure solution. Although only small 

 quantities of the liquids of the food cultures were introduced 

 with the food, nevertheless there must have been some initial 

 differences of a chemical nature between the experiment and 

 its control. The possible effects of these substances were not 

 tested, nor were they mentioned in Whitney's paper. Further- 

 more, it was probable that the organisms in the food cultures 



