194 w - v - LAMBERT, W. S. RICE, AND H. C. A. WALKER. 



these eggs hatched on September 29, and on October 1 two 

 parthenogenetic sisters were isolated. One became the mother 

 of what has been called race A and the other became the mother 

 of what has been called race B. The two sister parthenogenetic 

 races A and B were kept in Syracuse watch glasses. Usually 

 once in forty-eight hours five daughter-females of each race were 

 isolated, each daughter-female being placed in a separate watch 

 glass. They produced the young females of the succeeding 

 generation. Race A was fed on a pure culture of the flagellate, 

 Polytoma. This food was grown in horse manure solutions, 

 which was prepared as follows : eight hundred cubic centimeters 

 of fresh horse manure and one thousand cubic centimeters of 

 tap water steam sterilized for one hour. This was cooled and 

 diluted in the proportion of one part horse manure solution to 

 two parts of boiled rain water. Polytoma were then put into it 

 in an open pan and placed at about 18 C. The Polytoma grew 

 very quickly and in 24-48 hours immense numbers of them were 

 produced. This culture, ranging from 24-96 hours old, was 

 decanted and replenished daily — one part culture medium to two 

 parts boiled rain water being added. From the surface of this 

 culture the Polytoma were taken with a sterilized pipette. This 

 food was centrifuged so as to make it concentrated enough so 

 that one drop was sufficient for each watch glass containing a 

 female rotifer and a small amount of filtered rain water. 



Race B was fed both from the pure culture of Polytoma and 

 from two or three cultures of green flagellates, Chlamydomonas, 

 Chloroganium euchlorum, and Euglena. 



As some of the green food grew in salty cultures it was always 

 washed with rain water before being placed in the watch glasses 

 as food for the rotifers. 



During the whole period of fifteen months the two races have 

 been conducted in parallel generations. The external factors and 

 environment have been as near alike as it has been possible to 

 make them. The individuals of each generation were isolated 

 at the same time, were put into the same kind of watch glasses 

 and with approximately the same amount of filtered tap water, 

 the only difference being in the food. The watch glasses were 

 stacked side by side. During the day the room was lighted by 

 the north light. 



