274 DAVID DAY WHITNEY 



portion to the females from 10 per cent to 60 per cent. Dia- 

 grams of a male and a female and the different eggs are in figure 

 3. The details of the experiments are in table 2 and a plotting 

 of experiments 10 to 12, and 16 and 17, are in diagram 4. 



The Diaschiza sterea are bottom feeders eating only micro- 

 organisms that settle and remain on the bottom of the culture 

 dishes. As both Polytoma and Chlorogonium did this to a consid- 

 erable extent they furnished very good food material. Chlamy- 

 domonas was tried as a food but the rotifers soon died, appar- 

 ently from starvation. 



At this time another series of experiments was made to deter- 

 mine whether the males were caused to appear by the stimulus 

 of the new food or by the stimulus of the bouillon in which the 

 new food and the rotifers were placed. In order to determine 

 this point some culture water from the Polytoma cultures in 

 which the rotifers were thriving was filtered and the female 

 rotifers put back into it. Then the Chlorogonium which had been 

 cultivated in a bouillon solution (1 part of the stock bouillon 

 solution to 1 part water) were thoroughly washed by placing 

 them in test tubes filled with sterilized water and centrifuging 

 on a large centrifuging machine. This process would, of course, 

 collect the Chlorogonium in a small mass at the end of the tube. 

 This washing process was repeated three or four times until the 

 Euglena were undoubtedly thoroughly freed from any bouillon 

 on their external parts. These washed Chlorogonium were then 

 fed to the rotifers that had been put back into the filtered 

 Polytoma culture water. Males soon appeared and in some 

 experiments as many as 40 per cent were found. These experi- 

 ments demonstrate that the stimulus which caused males to be 

 produced was in the Chlorogonium itself and not in the bouillon. 

 The details of the experiments are in table 3. All the experi- 

 ments with this species of rotifer were done at room temperature 

 on a table in subdued light. 



Diglena catellina 



In July of 1915 a few females of the rotifer, Diglena catellina, 

 were found in some general mixed culture jars which were prob- 

 ably inoculated by a collection of various organisms collected 



