i82 Life Cycle of Hydatina Senta [Dec. 



of old food cultures. This one individual need scarcely surprise 

 US if we note the very high percentage of male-prodiicers in the 

 first two generations bred in spring water. Manure Solution does 

 not rigidly exckide male-producers. It is important to remember 

 this in the consideration of other experiments where various sub- 

 stances do not wholly prevent male-producers from appearing. 



3. Influence of alkalinity on the percentage of male-pro- 

 ducers. Experiment 23. It was found impracticable to rear the 

 rotifers in water that was even faintly acid, so several degrees of 

 alkalinity were used. A n/io Solution of NaOH in distilled water 

 was kept in stock in a tightly stoppered bottle. In making up this 

 Solution, no further precaution was taken to make the normality 

 exact than to weigh the solid hydroxid carefully, exposed to the air. 

 A w/25 Solution of HCl was made up by titration against the 

 NaOH Solution immediately after the latter was prepared, and was 

 kept in stock. Three grades of alkalinity were used in the experiment, 

 the Solutions being prepared as f ollows : Great Bear spring water, 

 which is itself alkaline, was used unaltered in one line ; for the 

 second line, the w/io NaOH Solution was diluted to ten times its 

 volume with Great Bear water; for the third line, the n/25 ^^1 

 Solution was diluted to forty times its volume with Great Bear 

 water. The alkalinity of the Great Bear water was not accurately 

 'determined, but was less than n/io, so that addition of n/io 

 -NaOH Solution increased its alkalinity ; neither was the alkalinity of 

 the diluted Solutions known. As it was necessary to expose the 

 NaOH Solution to the air while it was being used, the dilute Solu- 

 tion was made up daily. The data from this experiment are given 

 in Table 6, where the alkalinity increases from left to right. 



From this experiment it would seem that the greater the alka- 

 linity the fewer the male-producers, but the differences are too small 

 to draw a safe conclusion from one experiment. 



Experiment 24. The stock Solutions in this experiment were 

 produced in essentially the same manner as in the preceding experi- 

 ment, but in diluting them for daily use distilled water was used 

 instead of Great Bear water. The alkalinity of the final Solutions 

 was therefore more accurately known. It could not be exactly 



