EFFECT OF ENVIRONMENT UPON HYDATINA SENTA. 



337 



jar was being used daily for other experiments, the percentage 

 of oxygen used was not always the same. From May 27 to 

 June 22, and on July 8 (see Table I.), the atmosphere contained 

 40 per cent, of oxygen; on all other dates 60 per cent. 



In the other of the two dishes was placed untreated water. 

 This dish was also set under a jar sealed at the edges, to prevent 

 excess of evaporation, but in ordinary air. 



After 20 to 40 hours the dishes were removed and the number 

 of eggs at the surface film and at the bottom counted. As shown 

 in Table I., the eggs are much less abundant at the surface film 

 in the presence of much oxygen than in air. 



TABLE I. 



Showing the Number of Eggs Laid at the Surface Film and at the Bottom of the Dish 

 by Rotifers Placed in Air and in an Atmosphere Containing an Excess of Oxygen. 



Effect of oxygen upon the size of par theno genetic eggs. 

 Eggs laid by rotifers in oxygenated water, and in untreated 

 water, were obtained in the following manner. Three or four 

 young females, due to begin egg laying in 6 to 12 hours, were 

 placed in each of two watch glasses. One lot was immersed 

 in water saturated with an atmosphere of which 40 per cent, or 

 60 per cent, was oxygen, and then set under a bell jar in a similar 

 atmosphere. The other lot was placed in spring water, and the 

 dish was set under a closed bell jar in air. After 24 hours the 



