236 BESSIE NOTES 



Hydatina senta, ShuU and Whitney have shown that various 

 factors in the environment have an influence upon the propor- 

 tion of males appearing in any Une. The amount of oxygen in 

 the medium, the concentration of the food, the proportion of 

 various microorganisms available for food, and the concentration 

 of various chemicals seem to be factors associated with the 

 percentage of males, or of male-producing females, produced by 

 various mothers. 



In Proales, changes in the nature and concentration of the 

 food, changes in the temperature at which various cultures were 

 maintained accompained by changes in food, and changes 

 in the chemical constitution of the medium were introduced in the 

 study of the conditions under which the male form might be 

 produced. In a culture fluid of 3^ per cent malted milk, female 

 forms had consistently appeared throughout the study; so in- 

 creases in the concentration of the milk were made until solu- 

 tions of I per cent, j per cent, | per cent, and 1 per cent had 

 been used. In the higher concentrations bacteria developed so 

 rapidly that the medium soon became flocculent and less favorable 

 for a high egg production and greater length of life. On the 

 other hand, a decrease in the concentration of the milk to ^ per 

 cent and ^ per cent tended to decrease the available food to such 

 an extent that the number of eggs deposited decreased, although 

 the length of the life-cycle was not influenced. Males do not 

 appear in malted milk either in decreased or increased concen- 

 trations. Beef extract, made from Armour's bouillon cubes, 

 was made in | per cent, J per cent, and ^ per cent concentration. 

 The number of eggs produced in any of these percentages was 

 much lower than in the stock solution of malted milk and in no 

 case was there any change in the nature of the eggs or the organ- 

 isms produced. Pasteurized milk in ys per cent, and | per cent 

 concentrations was employed, but owing to rapid bacterial 

 action the solution became flocculent within a very few hours 

 at laboratory temperature; successive generations of rotifers 

 were maintained in it with difficulty and no males were produced. 

 A solution of horse manure made after WTiitney's ('14) formula 

 was prepared and used in the proportion of 1 part horse-manure 



