3SS 



THE AMERICAN NATURALIST [Vol. L 



tive overwork and season. White color could be ob- 

 tained from the later, "weaker" germs, though this color 

 did not appear in birds from the "stronger" germs of 

 the earlier season. And further, that white, or whitened, 

 "mutants" from pure breds were derived almost or quite 

 exclusively from those conditions which produce "weak- 

 ened germs." Among such conditions are late season 

 and overwork, inbreeding and great extremes of age- 

 either very old or very young. This brief outline of 

 Whitman's findings on sex is perhaps a more adequate, 

 and more accurate, one than I was able to give to one of 

 the societies represented here when I had only begun the 

 examination of this data in 1911. Two brief summaries 

 given on the chart (not given here) will assist in obtain- 

 ing a picture of the nature of the results. I may add that 

 by very strongly "overworking" females of some species 

 —overworking them more strongly than Whitman did— 

 I have been able to obtain a high predominance of females 

 during autumn from a cross merely of specific 2 value. 

 This result is illustrated by Chart II, though the matings 

 there exhibited were prepared for the primary purpose 

 ■of illustrating results in the study of size. It will be 

 noted in the chart that parents overworked in a previous 

 year throw a high proportion of females during the whole 

 of the succeeding year, and most markedly in late 

 autumn. In this mating the ratio at the end of the sea- 

 son is 14 females to 1 male; in the other (not previously 

 overworked) there was an excess of females only after 

 overwork-during the latter half of 1914 (7<M0?) ; and 

 in the year following this overwork there were 21 or 

 more females, to 11 or fewer males. Such data are not 

 exceptional ; they coincide with the usual. 



Now, in the generic crosses which give all, or nearly 

 all, males at the beginning of the season and all, or nearly 

 all, females in the autumn what is happening?— true sex 

 reversal? or is it selective fertilization, differential mat- 



