OXYGEN AND MALE PRODUCTION 475 



In a former paper it was shown how a high per cent of males 

 could be obtained by feeding Chlamydomonas in the sunlight, 

 and now opposite results are obtained! These contradictory 

 results are due to differences in manipulations of feeding and also 

 to different conditions of the Chlamydomonas itself as a food in 

 these two instances. In the former experiments the Chlamy- 

 domonas. were put into the culture water with the rotifers and 

 the rotifers fed upon them for only a few hours, during which 

 the Chlamydomonas were kept actively swimming toward the 

 lighted side of the dish as it was rotated upon a kymograph. 



In these later experiments the feeding conditions were quite 

 different. No rotation of the bottles was made, and when this 

 is not done many of the Chlamydomonas swim to the lighted 

 side of the dish and adhere to the surface of the glass. This 

 enables all such individuals to escape from being eaten by the 

 rotifers. Sometimes the rotifers were able to pick up only a 

 small number of stray Chlamydomonas in direct sunlight. On 

 cloudy days and in darkness the Chlamydomonas are more 

 active and are more available as food for the rotifers. In ex- 

 periment 6 of table 3 cloudy weather prevailed throughout the 

 last five days that the rotifers were in the experiment. Prob- 

 ably the Chlamydomonas remained active in the diffuse dayUght 

 so that the rotifers were enabled to feed upon them as readily 

 as in the darkness. This would explain why the per cent of 

 males is equal in each lot. 



When the Chlamydomonas remain in the sun for several 

 days in the old stable-tea culture water, which is devoid of all 

 nutritional substances, very little, if any, reproduction occurs 

 among them, but each individual becomes of full size and is 

 covered with a tough covering which renders it indigestible for 

 the rotifers. Consequently, if nearly all of the Chlamydomonas 

 attach themselves to the side of the dish, the rotifers are unable 

 to obtain a superabundance of food or, on the other hand, if 

 some of the Chlamydomonas remain active they develop such a 

 tough covering as to render them nearly unfit as food for the 

 rotifers. In either case the rotifers are not overfed in the sunlight. 

 While, on the contrary, in darkness all of the Chlamydomonas 



