MALE-PRODUCTION IN HYDATINA 523 



poured some spring water and scum from a manure solution 

 was added for food. The water put into the other dish was first 

 saturated, by continued agitation, with an air-oxygen mixture 

 produced by removing half the volume of air and replacing it with 

 oxygen. Such a mixture must have been composed of about 60 

 per cent oxygen and 40 per cent nitrogen. Manure scum was 

 added for food, as in the control dish. The dish was then placed 

 under a sealed bell jar, from which half the air was withdrawn 

 by a filter pump and replaced with oxygen. The air-oxygen 

 mixture under the bell jar must have consisted of about 60 per 

 cent oxygen and about 40 per cent nitrogen. ^ 



After twenty-four hours all the parents were removed from 

 these dishes. The young hatching from the eggs laid in that 

 period, experiment and control alike, were reared to maturit ^ in 

 untreated water with manure scum as food. Whatever differ- 

 ences they exhibit, therefore, are due to differences in the condi- 

 tions which affected the mother or early developmental stages. 

 Table 1 shows the results. The excess of male-production in the 

 presence of oxygen is fairly marked. 



Experiment 2. This experiment was designed to contrast the 

 effects of 60 per cent and 40 per cent oxygen mixtures by two 

 simultaneous tests. In the absence of a second suitable bell jar, 

 one test was made with 60 per cent oxygen, the next test with 40 

 per cent oxygen. It was hoped that by this alternation an epi- 

 demic of male-production, if one occurred, would occur in the 

 control of both series of tests. Since, however, it was not feas- 

 ible to make one test each day, and several days usually elfi,psed 

 between tests, that object was only partially attained. It 

 happened that on the whole the line used for control produced 

 more male-producers on the days when 60 per cent oxygen was 

 employed than on the days on which the 40 per cent mixture was 

 used. How much this circumstance vitiates the conclusion to be 

 drawn from the experiment is not known. 



-The method of procuring air-oxygen mixtures of a given composition is here 

 stated again specifically, since Whitney seems to have misunderstood the 

 expressions '60 per cent oxygen' and '40 per cent oxygen.' 



