188 Experiments on the Rotifer Hydatina 



bottom of the tube and as much liquid as possible was drawn off with 

 a pipette, then spring water was added. The process was repeated 

 several times until it could be assumed little or no horse manure 

 solution remained. Judging from Shull's^ results, it was thought this 

 method would give a very definite increase in arrhenotokous females, 

 as the horse manure liquid was practically removed ; but very few were 

 hatched. The rotifers were kept well supplied with fresh protozoa 

 during this experiment. Again, the temperature was varied, the horse 

 manure solution was oxygenated, but no definite change in the pro- 

 portion of the sexes' could be produced. 



During one period of the testing of the family given in detail above 

 no arrhenotokous females were produced. A very concentrated solution 

 of horse manure was used but it was not an old solution. This was 

 suspected of producing the results and on the completion of the test 

 rotifers were bred in a highly concentrated solution of horse manure 

 which was swarming with protozoa. The solution was more concen- 

 trated and the protozoa more numerous than in any test previously 

 made. No arrhenotokous females were produced by these rotifers. 



I then decided to try the effect of a culture of green protozoa used 

 as food instead of the colourless protozoa in the horse manure solution 



1 Journ. Exp. Zool. 1911. 



