DAVID D. WHITNEY. 



is probably due to the fact that the former strain had been 

 reproducing parthenogenetically for several years and had 

 become weakened whereas the latter strain was developed from 

 a resting egg in November, 1914, and at the present time is as 

 vigorous as at first. 



The method of making the media and rearing the two kinds 

 of protozoan food cultures has been given in detail in a former 

 paper and will not be repeated here, excepting a few additional 

 words about the green food. When the Chlamydomonas had 

 been 2-3 weeks in the same media the individuals were large 

 and more or less quiescent. In this condition they were only 

 moderately effective although in one or two instances some 

 that had been two to three months in the same media were very 

 effective. When they had been in new bouillon media for 2-7 

 days with considerable sunshine at a temperature of about 

 28 C. they were of various sizes and seemed to be the most 

 effective. However, there seems to be a considerable amount of 

 chance in getting the Chlamydomonas in the optimum condition 

 for every experiment. This probably explains the varying per- 

 centages of the male-producing females obtained in the different 

 experiments. 



As it seems that the effect of a uniform diet on this rotifer has 

 not been sufficiently emphasized the following Table (I.) con- 



TABLE I. 



SHOWING THAT A CONSTANT AND UNIFORM DIET OF THE COLORLESS PROTOZOA, 



Polytoma, REPRESSES THE PRODUCTION OF MALE-PRODUCING FEMALES 



AND CAUSES THE PRODUCTION OF FEMALE-PRODUCING FEMALES. 



Kepi on a Uniform Polytoma Diet. 



cerning this point in three pedigreed races has been compiled 

 from the records in an earlier paper. 1 This shows that a con- 

 stant and uniform diet of Polytoma, has repressed the production 

 of males for nearly 300 generations. The long period of time 

 1 BIOL. BULL., Vol. 22, March, 1912. 



