LIFE CYCLE OF HYDATINA SENTA 



125 



the present section. The manure solution was boiled ; it was evapo- 

 rated to dryness and redissolved ; it was evaporated to dryness and 

 extracted with ether and alcohol; and it was decolorized by boil- 

 ing with animal charcoal. The following experiments show the 

 results of these operations in detail. 



Experiment XIX. Boiling the manure solution. After the 

 manure solution from an old food culture, made up with spring 

 water, had been filtered through a Berkefeld filter, part of the 

 filtrate was boiled gently for four minutes. The loss of volume by 

 evaporation was restored with distilled water. The remainder of 



TABLE 21 



Showing the number of male- and female-producers in the progeny of three sister 

 individuals of Hydatina senta, one line being bred in boiled filtrate of old food 

 cultures, one in unboiled filtrate, the third in spring water. 



the filtrate was not treated. The boiled filtrate was kept in stock 

 and was boiled every day until exhausted, chiefly to prevent the 

 development of bacteria. The unboiled filtrate was secured daily 

 just before using. Three pure lines of rotifers derived from sisters 

 were reared in April, 1910, one in boiled filtrate, one in unboiled 

 filtrate, the third in spring water. The results are given in table 

 21. The boiled filtrate has precisely the same effect as the un- 

 boiled. The substance in feces which prevents male-producers 

 from appearing is not, therefore, an enzyme, nor bacteria, nor 

 any other substance destroyed by boiling temperature. 



