342 • RIDDLE : CONTROL OF SEX RATIO . - 



female-producing tendency. These ovaries have sometimes 

 weighed half or more than half as much as the adult left ovary 

 with which they were associated, and have been found in such 

 birds dead at all periods from a few days to twenty-four months. 

 We here attempt no adequate description of this situation, but 

 one can not have observed the frequency of the persistence of 

 this ovary in the birds hatched from the eggs otherwise known 

 to be the most feminine from these overworked series, without 

 conviction that the same pressure which carries the eggs of 

 spring from male-producing to female-producing levels, also 

 carries the earlier female-producing level to another yet more 

 feminine. 



The several kinds of facts just reviewed in connection with 

 Chart 1 afford clear evidence that sex and characteristics other 

 than sex such as fertility and developmental energy not only 

 bear initial relations to the order of the egg in the clutch, but 

 that sex and these other characteristics are progressively modified 

 under stress of reproductive overwork, until at the extreme end of 

 the season certain aspects of femininity are abnormally or un- 

 usually accentuated. In the light of these facts sex reveals 

 itself as a quantitative modifiable character. And an associa- 

 tion of modifiable metabolic levels with the flux and change of 

 sex, or of sex ratios, has been found and described in precisely 

 this same connection. 



Let us now take these facts with us in a rapid survey of some 

 experimentally induced and puzzling sex-ratios, and also into 

 a brie? consideration of some important facts of sex that have 

 been learned from embryonic and post-natal stages of organisms. 



The evidence that higher water values and higher metabolism 

 are associated with male-producing eggs, lower water values 

 with female-producing eggs, is of first importance in connection 

 with our own generalization as to the germinal basis of sex- 

 difference; and is further of much interest as being the means 

 of demonstrating that in the — as I believe — several valid cases 

 of sex-control now known, one thing in common has really been 

 effected; this, though the work has been carried out on a con- 

 siderable variety of animals and though the procedures have 



