200 W. V. LAMBERT, W. S. RICE, AND H. C. A. WALKER. 



of young of A and C was marked. The average period of growth 

 and reproduction was 63.6 hours, during which period the 

 average number of young of the A race was 6.86; of the B, 9.35; 

 and of the C, 8.66. The complete tabulation of results may be 

 found in Table VII. 



Table VII. 



The three races were then carried on side by side. Since the 

 145th generation the green food given Race B has been made up 

 for the most part of Euglena, in place of the Chlamydomonas 

 heretofore used. About the same time as the change in the 

 green food the centrifuging of the Polytoma culture was discon- 

 tinued and more drops of the unconcentrated food given instead. 

 After the seventh series of observations, the investigators began 

 to encounter difficulty with the supply of Polyloma. However, 

 all three races of rotifers continued to reproduce partheno- 

 genetically, although with slightly less than usual vigor in Race 

 A. Nevertheless, notwithstanding all care possible in feeding, 

 isolation and temperature the A race, fed only Polytoma, died 

 out with the 198th generation, probably due to the faulty 



