294 DAVID DAY WHITNEY 



males but when they were put upon the green diet at the same 

 temperature they produced many males. In the experiments 

 with Pedalion mirum and Branchionus pala which were carried 

 on partly in direct sunlight the temperature varied from 20°C. 

 to 37°C. on nearly every day because both sets of experiments 

 were carried on, luckily, in periods of many successive days 

 of sunshine. When the green flagellates were scanty or in the 

 mature stages, regardless of the daily changes in temperature 

 from room temperature to 37 °C. during the mornings and from 

 37°C. to room temperature during the evenings, very few male- 

 producing females were produced. However, when fresh Chlam- 

 ydomonas culture media was added to the jars in which the 

 rotifers were living an enormous increase in the numbers of 

 Chlamydomonas occurred and soon, in some jars, as high as . 

 95 per cent of male producing females were found. In former 

 observations upon Hydatina senta it has been noted that at the 

 higher temperatures of about 25°C. to 28°C. its green food was 

 very active and could be readily obtained by the rotifers and 

 as many as 80 per cent produced were male-producers but at 

 the lower temperatures of 9°C. to 12°C. the greater part of its 

 green food became quiescent in which stage it was impossible 

 for the rotifers to eat it and all the females produced were fe- 

 male-producers. The general conclusion can be drawn that the 

 changes in temperature unless accompanied by changes in the 

 amount of the diet are not potent factors in regulating the 

 production of female and male-producing female rotifers. 



SUMMARY 



1. In pedigreed cultures of Hydatina senta a diet of the color- 

 less flagellate, Polytoma, which is probably a poor diet, causes 

 only female-producing daughters to be produced, whereas a diet 

 of the green flagellate, Chlamydomonas pulvisculus, which is 

 probably an optimum food, causes nearly all male-producing 

 daughters to be produced. 



2. In mass cultures of Brachionus pala a scanty diet of miscel- 

 laneous green flagellates caused nearly all female-producing fe- 



