322 D. D. WHITNEY. 



The two weak races, A and B, which have been fully described 

 in a former paper were used in these experiments. The criterion 

 of weakness was the rate of reproduction. Races A and B in 

 the spring of 1911 were allowed to produce close-fertilized eggs 

 in the 37Oth and the 38oth parthenogenetic generations respec- 

 tively. From these close-fertilized eggs females developed which 

 reproduced parthenogenetically for a time but by the end of the 

 summer they had been allowed to close-breed three or four times. 

 At this period most of the experiments described in this paper 

 were undertaken. 



Ever since the two races were started in the fall and winter of 

 1908 and 1909 they have been subjected to a very constant 

 environment. They have been kept at room temperature rang- 

 ing from 1 8 C. to 22 C. and always have been in a food solution 

 of horse manure. During the last sixteen months of their 

 parthenogenetic propagation they were even fed upon a pure 

 culture of the flagellate, Polytoma, which was reared in a horse 

 manure solution. A certain quantity of this horse manure 

 solution containing the protozoa was added to a certain amount 

 of tap water and placed in Syracuse watch glasses thus making 

 the amount and concentration of the food culture water in which 

 the rotifers lived practically constant. 



DIFFERENT FOOD MATERIALS. 



In order to cause a great variation in the food factor and 

 also of the chemicals in the water food cultures were prepared 

 from the feces of various herbivorous, carnivorous and omni- 

 vorous animals. These food cultures were made in battery 

 jars and inoculated with a miscellaneous lot of protozoa from 

 several small fresh water ponds. The rotifers were placed in 

 these large jars and allowed to live freely from 9 to 19 days and 

 then were transferred to other food jars which contained feces of 

 a different animal. In this manner a great variation of protozoa 

 and of chemical substances in the water were obtained. These 

 experiments extended through about three months. Table I. 

 shows the data obtained at the end of the experiments which 

 demonstrate that no reinvigoration had taken place in either of 

 the two weak races. 



