476 



DAVID D. WHITNEY 



remain active and small and do not develop the tough covering. 

 Thus there is a fine food supply for the rotifers for several days. 

 The matter of the food supply probably explains the sex ratio. 

 When the supply is good as in darkness more males are produced 

 and when it is poor as in sunlight fewer males are produced. In 

 all of these experiments in the sunlight much free oxygen was 

 given oE during the day and rose to the surface forming a frothy 

 scum. 



Table 4 shows the light conditions throughout these experi- 

 ments. 



TABLE 4 

 Showing light conditions of the days during the experiments in table 3 



Table 5 shows the details and results of another set of experi- 

 ments in the sunlight and darkness in which the quantity of free 

 oxygen in the culture water was determined both at the be- 

 ginning and at the end of many of the experiments. The 

 amount of the food was more accurately measured than in the 

 experiments of table 3. Small amounts of Chlamydomonas, 0.10 

 cc, and of Polytoma, 0.05 cc, were put into 10 cc. of the culture 

 water and well stirred. Then 3 cc. of this mixture was added 

 to 50 cc. of the filtered old stable-tea culture water. To the lot 

 that was placed in sunlight 0.2 to 1 cc. of additional Chlamy- 

 domonas was added. Each lot was divided into three portions 

 and put into three vials, 1 inch diameter, and allowed to stand 

 twenty-four hours and then three or four rotifers were added. 

 These experiments were started in the morning and thus afforded 

 an opportunity for the Chlamydomonas to generate sufficient 

 oxygen in the sunlight to quite thoroughly charge the culture 

 water with it before the rotifers were added. It also enabled 

 many of the Chlamydomonas to become attached to the sides 



