330 



riddle: control of sex ratio 



as my first lots of yolk samples were placed on the balances for 

 the preliminary weighings. The balances alone and at once 

 showed that the mass of the yolk of the first egg of nearly all 

 pairs of eggs (from pure species) was less by from (usually) 9 

 per cent to 15 per cent than the mass of the yolk of the second 



TABLE 6 

 Weight of Entire Eggs, and op Yolks, 1913-1915 of 9 641 and 9 647 



a The entire egg loses weight on standing; the yolk gains weight on standing. 



egg of the pair. There were occasional reversals of this relation 

 and also occasional pairs with quite nearly equivalent weight. 

 In the eggs produced by hybrids this relation did not obtain at 

 all. Illustrations of these differences in weight between the egg- 

 yolks of first and second egg of the clutch may be seen in any of 



