EFFECT OF ENVIRONMENT UPON HYDATINA SENTA. 



339 



accumulation of metabolic products did not affect the time of 

 development of the eggs unequally, the water in the control dish 

 was also drawn off after the rotifers were removed and replaced 

 with fresh water. This dish was then set under a bell jar in air. 

 The next morning the two dishes were examined at intervals 

 of 20 to 30 minutes, and the young rotifers removed and counted 

 as they hatched. In this way the approximate time of develop- 

 ment of the eggs was determined. In Table III. these times are 

 collected in groups, to the nearest half hour. When these 

 figures are treated statistically, they compare with one another 

 as in Table IV. 



TABLE III. 



Showing the Time Required for Development of Eggs in Oxygenated Water and in 

 Untreated Water, 



TABLE IV. 



Showing the Time of Development of Eggs in Oxygenated Water and in Untreated 

 Water. Statistical Treatment of Data in Table III. 



The eggs in oxygenated water hatched in a trifle shorter time, 

 and somewhat more uniformly, though the difference in each 

 case is so small that it may be insignificant. The greater uni- 

 formity of the time of development in oxygenated water (second 

 line of Table IV.) is not improbably significant. 



Effect of Oxygen upon the Contraction of the Foot Muscles. 



Rotifers were placed in water saturated with an atmosphere 

 containing 40 per cent, of oxygen, under a bell jar containing a 

 similar atmosphere, and kept there 24 hours. They were then 



