338 



A. FRANKLIN SHULL. 



watch glasses were removed, and all the eggs that were in a 

 horizontal position were measured by means of a screw microm- 

 eter eye-piece. The measurements are given in units of the 

 scale. They are directly comparable with the measurement of 

 eggs in my former paper (Shull, 1915) since all the measurements 

 were made with the same microscope and with the same lenses. 

 The mean length, mean breadth, standard deviation, etc., 

 of the two lots of eggs are given in Table II. 



TABLE II. 



A Comparison of the Eggs Laid by the Rotifer Hydatina Senta in Oxygenated Water 

 and Untreated Water. 



The eggs in the oxygenated water were a trifle larger than those 

 in the untreated water, though it can hardly be said that the 

 difference is statistically significant. However, a difference that 

 cannot be proven by statistical treatment to be significant is not 

 necessarily insignificant. It seems to me not improbable that 

 the difference in length is significant, but it is very small in com- 

 parison with the difference between English and Nebraska eggs 

 described in my earlier publication (op. tit.}. 



Effect of oxygen upon the time of development of par theno genetic 



eggs. 



A number of egg-laying females were put into each of two dishes 

 in the evening. In one dish was placed ordinary water, in the 

 other water that had been oxygenated in the manner described 

 in the preceding experiments. The females were removed after 

 about an hour, but the eggs which they had laid were left in the 

 dishes. The oxygenated water in one dish was then removed 

 and replaced with fresh oxygenated water, and the dish was set 

 under a bell jar in an atmosphere containing an excess of oxygen 

 (40 or 60 per cent.). To insure that mechanical disturbance or 



