SOME EXPERIMENTS ON THE ROTIFER 

 HYDATINA. 



By EDITH E. HODGKINSON. 



Six years ago I began some tests and experiments on the rotifer 

 Hydatina which were brought to a close in the summer of 1913- 

 The principal object was to test for strains producing no arrhenoto- 

 kous females. Many tests were made but arrhenotokous females 

 occurred in all the families tested ; no pure theljrtokous strain was 

 found. The Rotifers were isolated in watch glasses during the tests 

 and the food used was a horse manure solution prepared in the same 

 way as that used by Whitney^ for his experiments on Hydatina. The 

 results of the testing of one family are given in the table below (p. 188). 

 The rotifer laid 42 eggs six of which hatched into arrhenotokous females. 

 The descendants of the thelytokous females from these eggs were tested 

 through a varying number of generations. The generations were rarely 

 completed. The table shows the number of generations tested from 

 each female and the number of thelytokous and arrhenotokous females 

 in these generations. 



Out of the thelytokous females tested all gave arrhenotokous females 

 in the first generation except I, XXXIV and XXXIX and these gave 

 them subsequently. 



Attempts were made to alter the relative proportion of arrhenotokous 

 and thelytokous females by using solutions of horse manure of different 

 ages and concentrations, but the results were not definite. Other 

 methods were tried to produce an increase in the number of arrheno- 

 tokous females but also with no definite results. Protozoa bred in 

 horse manure solution were removed from the solution and put in 

 spring water and these served as the liquid and food for the rotifers. 

 The protozoa were removed from the horse manure solution by centri- 

 fuging some of the solution in a tube. The protozoa sank to the 



1 Science, xxxii, No. 819, 1910. 

 Journ. of Gen. vii 13 



