268 DAVID DAY WHITNEY 



fresh bouillon was added the whole culture of the flagellates and 

 rotifers became balanced, that is the flagellates reproduced at 

 such a rate as to keep the rotifers moderately supplied with food. 

 When they were thus supplied moderately with food only fe- 

 males were found in the culture jar but when fresh bouillon was 

 added to the general culture it furnished additional food for 

 the flagellates causing them to multiply very rapidly and to 

 produce enormous numbers of themselves in the jar. With 

 this great increase of food the rotifers also began to eat raven- 

 ously and soon produced a great number of females which to 

 a large proportion produced male offspring. In this manner 

 of increasing the food by adding fresh bouillon males could be 

 produced in enormous numbers within a short time. These 

 males copulated with many of the young females and within 

 a few days the majority of the adult females were carrying fer- 

 tilized eggs. Soon the cultures were depleted of food by the 

 great increase of rotifers and then nearly all the rotifers died of 

 starvation but left thousands of fertilized resting eggs. 



It has been shown by Lauterborn that if the male egg is fer- 

 tilized in Asplanchna it produces the winter or resting egg. 

 The same fact has been shown by Whitney and Shull to be 

 true of Hydatina senta and recently it has been shown by Moro 

 to be true also of Brachionus pala. 



These experunents were done in mass cultures many of which 

 contained many thousands of individuals and countings were 

 made of the female-producing and male-producing females at 

 various intervals. These two kinds of females were easily dis- 

 tinguished from each other because after they had extruded 

 the eggs they carried around the eggs attached to their bodies. 

 The male-producing females carried small eggs and the female- 

 producing females carried large eggs. The details of the experi- 

 ments are in table 1. Drawings of the females carrying the 

 different eggs and also of a male are in figure 2. In diagram 2 

 a plotting is seen of experiment 1, and in diagram 3 a plotting 

 is seen of a part of experiment 3. 



