riddle: control of sex ratio 333 



the appended tables in which yolk weights are given (Tables 4, 

 5, 6, 7, 8). 



Other facts concerning the yolk weights which soon came to 

 light were, that the yolks from an individual bird become larger 

 in the autumn, particularly if the bird is made to lay numerous 

 eggs (i.e., overworked) during the season. A schematic repre- 

 sentation of the dimorphism of the ova, and of their increase in 

 size from spring to autumn is shown (under 1) in Chart 1. A 

 further fact of kindred nature was learned when the study was 

 extended over a period of years, namely that the egg-yolks of 

 an individual bird tend to become larger as the bird grows older; 

 the yolks of the spring, however, are usually smaller than those 

 of the previous autumn, though larger than those of the previous 

 spring (Table 6). These facts are now established by accurate 

 weighings of more than 12,000 yolks, freed and separated from 

 their surrounding shell and albumen. 



The details of the chemical analyses of one series of eggs ob- 

 tained in 1912 are given in Table 7. These details we need not 

 here consider, but it will be observed that we find larger amounts 

 of the various chemical fractions (excepting water) in the fe- 

 male-producing egg than in the male-producing egg. This 

 holds true alike for the female-producing egg of the clutch, and 

 for the late eggs, which under these conditions are predomi- 

 nantly female-producing, as compared with the group of earlier 

 eggs which under the conditions of the generic cross are rela- 

 tively male-producing. 6 Not only does the size of the egg in- 

 crease with its later position in the series, i.e., with lateness of 

 season, as shown by a mere comparison of the yolk weights of 

 such a series of eggs, but the percentage of energy-yielding or 

 stored materials increases as much, or probably more, than is 

 indicated by the size, or net weight of the yolk. The per cent- 

 age of water, we shall later see, is greater in the male-producing 

 eggs. 



For our present purpose the importance of the results of these 

 and other analyses is that they conclusively show: (1) that the 



6 In this particular series, 8 of the first 9 eggs incubated produced males; the 

 egg of this group that hatched a female was "a very large egg." The last three 

 hatches were females. 



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