340 riddle: control of sex ratio 



were prepared originally to make clear certain observations on 

 size of off-spring in relation to their origin from eggs produced 

 under overwork, after continued overwork, and in relation to 

 the order of the eggs in the clutch. The tables themselves 

 tell much of their story and we here forego a further considera- 

 tion of them (see Riddle, '16, p. 406). 



The seventh curve of Chart 1 refers to a long and rather 

 large series of tests of the sex-behavior of series of birds such 

 as those whose origin is indicated in Table 3 (series of 1908). 

 We have here an opportunity to study and compare sex phe- 

 nomena of particular birds whose sex we have reason to believe 

 had been reversed from its initial sex-tendency; that is to say, 

 where successive pairs of females have originated from succes- 

 ive pairs of eggs in the autumn, under overwork, we have the 

 reasons already given for believing that some or most of such 

 females arising from first eggs of the clutch have had their 

 metabolism depressed to a point sufficient to make them fe- 

 males; but the second eggs of the same clutches should by the 

 same means have been carried to a still more "feminine" level; 

 and though both are females, it seemed possible to differentiate 

 the one sort from the other, and this has been successfully done 

 in a series of tests which now extend through a period of nearly 

 five years. Each female has been given about nine tests, each 

 of six months duration, with (for the most part) another female. 



In this study, then, female is mated with female and male 

 with male. Such pairs, from a very few selected pairs of par- 

 ents, are kept mated for a period of six months. Most of the 

 birds used, for lack of success with the incessantly fighting 

 males, have been females, and most of the nine or ten successive 

 tests with each bird have been made with her own sisters. The 

 members of the pair are kept apart except when under obser- 

 vation; when put together, as is done twice daily, the records 

 are taken of those females of the pair which behave as males 

 in copulating with their mates. Three facts are definitely es- 

 tablished by the data obtained: (1) The females of the orient- 

 alis X alba cross (they are dark in color) are more male-like in 

 their sex behavior than the females of the reciprocal cross (these 



