INFLUENCE OF FOOD IN CONTROLLING SEX 549 



cooked in a steam sterilizer at 10 to 15 pounds pressure for one 

 hour. The hquid part was then pressed out and usually equalled 

 1000 cc. This was put into a flask with a cotton plug and 

 sterilized. This could be kept indefinitely and used as a stock 

 supply provided it was sterilized each time after it was opened. 

 One part (100 cc.) of this liquid was added to three parts (300 cc.) 

 of sterilized water, inoculated with a few Polytoma and placed 

 in a large flat dish, thus giving a large surface of the culture water 

 exposed to the air. Within 2 to 3 days the culture water would 

 be teeming with the Polytoma but after a day or two the culture 

 became spent and only a few Polytoma would be found. When 

 this culture was about three days old one-half of it was poured 

 off and 100 cc. of the stock supply of the manure liquid and 300 cc. 

 of sterilized water were added. Eighteen to twenty-four hours 

 later countless numbers of the Polytom.a could be taken off from 

 the surface with a pipette. This process of pouring off one- 

 half of the old culture water and adding new medium was re- 

 peated every day and in this way a vigorous food culture of 

 Polytoma was continuously maintained for the rotifers at room 

 temperature. 



Female rotifers of various ages were taken from the controlled 

 female strain, which produced nearly all females through twenty- 

 five generations by being fed upon a continuous diet of Poly- 

 toma, and fed the green flagellate, Dunaliella, by the method as 

 described earlier in this paper. 



Tables 1 to 5 show the important results obtained in a long 

 series of observations. 



Experiments 1 to 23 have been omitted because they were 

 made when the methods of feeding were being perfected and 

 consequently did not show as favorable results as the later 

 experiments. Experiments 24 to 63 include all the other experi- 

 ments which were made in a successive series. A large number 

 of individuals, considering the amount of work that each one 

 entailed, has been observed, as recorded in tables 1 to 3. 341 

 mothers produced 5562 daughters, of which 3 per cent were male- 

 producing daughters when reared under the influence of Poly- 

 toma diet, and of which 57% were male-producing daughters 



