riddle: control of sex ratio 335 



females store more materials, and — as has been noted — yield a 

 higher percentage of females, than do birds not old. 7 There- 

 fore, it is evident that the egg of female-producing tendency is 

 one whose storage metabolism is high, as compared with eggs of 

 male-producing tendency. Moreover, the analyses show that 

 during the season successive clutches present higher and higher 

 storage, i.e., the earlier clutches store less — are more male-like; 

 the later ones all store more — are more female-like — and as al- 

 ready noted the eggs of the low storage period give rise (in the 

 generic cross) to males, and those of the high storage period 

 produce females. 



We here obtain a close view of that upon which sex difference 

 rests. And the facts are now quite beyond question. Un- 

 mistakably, less storage and high storage pertain respectively to 

 the male- and female-producing germs. Unmistakably, our pro- 

 cedures, connected with generic cross, season, and overwork, 

 delivers males from the smaller storages in the earlier eggs. Un- 

 mistakably, the procedures raise the storage in all of the later 

 eggs, and unfailingly we then find that these eggs yield only, or 

 predominantly females. And if we eliminate the factor of wide 

 (generic) cross and mate the female with one of her own or a 

 very closely related species (Table 5), then we see that the pro- 

 duction of males and females coincides from the first with two 

 storage values — with two sizes of eggs (yolks) in the clutch — 

 males from the smaller first, females from the larger second. 

 Only after overwork and season have raised the storage value 

 of the eggs is this situation seriously disturbed. And the dis- 

 turbance — associated with an increase in the storage metabolism 

 of all the eggs — delivers as before, an excess of female offspring 

 (Tables 4, 5, 6). 



The progressive increase in storage capacity of the eggs during 

 the season — under overwork — is to be interpreted as a decrease 

 in the oxidizing capacity of these same eggs. Living cells in 

 general dispose of ingested food material by storing it or by 

 burning it. If oxidized the products of the oxidation are re- 

 movable and do not serve to increase the bulk of the cell. The 



7 See Tables 4, 5, 6. 



