EFFECT OF ENVIRONMENT UPON HYDATINA SENTA. 



341 



muscles in oxygenated water than in untreated water, but the 

 difference is rather small compared with its probable error and in 

 view of the crudity of the method of measurement may be without 

 significance. 



Effect of Temperature upon the Laying of Eggs at Surface and 



Bottom. 



Equal numbers of rotifers were placed in a number of dishes 

 of water. Some of the dishes were kept at room temperature 

 which was fairly constant at 20 to 22 C. Other dishes were 

 kept much cooler by setting them on a window sill outside. 

 A thermometer was kept beside the latter dishes, and was fre- 



TABLE VII. 



The Number of Eggs Laid at the Surface Film and at the Bottom at Room Temperature 

 and at Considerably Lower Temperatures. 



quently read. In Table VII., which gives the number of eggs 

 laid at the surface film and at the bottom, the stated temperature 



