MALE-PRODUCTION IN HYDATINA 143 



On the basis of the Spirogyra experiments as a whole, we are 

 unable to draw a definite conclusion. While by continuous 

 rearing with Spirogyra an increase in the number of male- 

 producers was one time obtained, at another time the increase 

 was practically zero; while when only the parents were reared 

 in Spirogyra cultures, the offspring were slightly less frequently 

 male-producers than in the control. 



Effect of oxygen 



The effect of oxygen was directly tested in several experiments. 

 The method, in general, was to put the rotifers into a dish of 

 water previously saturated with a mixture of air and oxygen 

 containing a known proportion of oxygen, then set the dish in 

 an atmosphere containing the same proportion of oxygen. The 

 two atmospheres used were composed, respectively, of 40 

 per cent and 60 per cent oxygen. The oxygen was obtained 

 by heating potassium chlorate with manganese dioxide and col- 

 lecting the gas in a gas holder over water. No attempt was 

 made to purify the oxygen. 



The 40 per cent oxygen atmosphere for saturating the water 

 was obtained by lowering a graduated tube, fitted at one end 

 with a stop-cock and open at the other end, into a vessel of 

 water, admitting first three volumes of air, and then one volume 

 of oxygen frdii the gas holder. The mixture was subsequently 

 driven into a flask of spring water inverted over water, and later 

 shaken repeatedly with the water remaining in the flask. When 

 the rotifers were put into a dish of this oxygenated water, the 

 dish was set under a bell jar made air-tight at the bottom with 

 a vaseline-coated rubber gasket. .By means of a filter pump, 

 one-fourth of the air under the bell jar was removed, as indi- 

 cated by a mercury manometer in connection ^\dth the bell 

 jar. Oxygen from the gas holder was then admitted until the 

 mercury fell to zero. The partial exhaustion and refilling of 

 the bell jar occupied usually less than two minutes. The 60 

 per cent oxygen atmosphere was obtained in the same way, 

 except that equal parts of air and oxygen were mixed. 



