39 2 



Experimental Zoology 



more girls are born. Other writers have published statistics 

 that give exactly contrary results. Geddes and Thomson give 

 such data in the following table : 



It will be seen that while three other statisticians obtained the 

 same kind of results as did Hofacker and Sadler, two others 

 give exactly opposite results. Contradictory evidence has also 

 been given for horses and sheep. As Schultze points out, the 

 results may mean, if they mean anything, that the conditions 

 do not determine the production of one sex or the other, but the 

 survival of an excess of one or the other kind of egg. Bidder 

 has shown in the case of women under 18 years of age bearing 

 children that there is an excess of boys in the proportion of 133.9 

 boys to 100 girls. 



Schultze tried to test this problem experimentally. Sexually 

 immature female mice were placed with males of the same age, 

 so that at the first period of heat conception might occur. The 

 females at this time were between 10 and 15 weeks old. There 

 were produced in all 60 males and 65 females. In other cases 

 the females were isolated and first allowed to breed after the 



