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A. FRANKLIN SHULL AND SONIA LADOFF 



scious, on our part, since the order was determined long before 

 it was known which ones would be male-producers. 



The number of groups of successive daughters, of one to five 

 members, comprising only male-producers, is summarized in 

 table 15. The slight increase in the mean number of male- 

 producers per group in the oxygen line is not in proportion to 



TABLE 15 



Showing the number of times that groups of one, two, three, four, or five successive 

 members of the families in table 14, were male-producers 



the increase in the total number of male-producers in that line. 

 The additional male-producers called forth by the oxygen ap- 

 pear, therefore, in additional groups of small size, rather than 

 as additional members of the groups which would otherwise 

 appear. Thus, there is an increase in the number of groups, 

 rather than an increase in the size of the groups. This means 

 a more uniform distribution of the male-producers through 

 their respective families in the oxygen line. 



Experiment 18. Continuous rearing in 60 per cent oxygen. This 

 is a repetition of Experiment 17, but with an atmosphere of which 60 

 per cent was oxygen, instead of 40 per cent. The methods used were 

 otherwise the same. Table 16 gives the results by generations. There 

 is no increase in the number of male-producers in the oxygen line; 

 whether the slight decrease is significant is not known. 



Although there is practically the same proportion of male- 

 producers in both lines in this experiment, the distribution of 

 these male-producers over the families is more uniform in the 

 oxygen line than in the control. This is shown first by the 

 number of male-producers occupying successive places in the 



