128 A. FRANKLIN SHULL 



continued in the middle of the second generation, hence the de- 

 tailed results are not of value. It may be said, however, that 

 the first family reared in the alcohol-soluble portion contained 

 a considerable number of male-producers. 



Experiment XXII. Decolorized filtrate. It was noticed in the 

 preceding experiments of this section that those residues which 

 produced the same effect as the unaltered manure solution were 

 brown like the original; those that had no effect were colorless. 

 To determine whether the substance producing the brown color 

 has any effect on the life cycle of the rotifers, a portion of the 

 filtrate from old food culture was decolorized with animal char- 

 coal. An excess of the charcoal was added to the filtrate, and 

 the mixture boiled eight or ten minutes. It was then filtered 

 through paper, and the volume of water lost by evaporation was 

 restored, the added water being passed through the filter. More 

 charcoal was added to the filtrate, and the boiling repeated. After 

 three or four boilings the filtrate was practically colorless. It was 

 not to be expected that the colored substance was the only one 

 removed by this process for animal charcoal probably carries 

 down most substances to some extent. But if the colored sub- 

 stance is wholly responsible for the non-occurrence of male- 

 producers in a manure solution, such a decolorized solution should 

 yield the same proportion of male-producers as pure water. 

 Whether it does or not may be seen from table 24. The experi- 

 ment was performed in May, 1910, with rotifers descended from 

 a winter egg collected in Grantwood, N. J., in April, and kept in 

 an ice-chest for a month. 



Even the decolorized filtrate greatly reduces the proportion 

 of male-producers, though not as much as the merely boiled filtrate. 

 Whether the 7 per cent difference between the decolorized filtrate 

 and the boiled filtrate is due to total removal of the colored sub- 

 stance or to partial removal of some other substances, can not 

 be decided from this experiment alone. That the latter is the 

 case, at least in part, will appear later, when it is shown that cer- 

 tain other substances which are presumably present in the manure, 

 and which were probably carried down mechanically by the char- 

 coal, do reduce the percentage of male-producers. This does not 



