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THE AMERICAN NATURALIST [Vol. L 



for the seasonn 1 difference in sex-production on the basis 

 of a differential maturation? The fact that the sperm is 

 present in the pigeon's egg during the whole of the 

 second maturation division may properly raise this ques- 

 tion. On this point we must say that the particular data 

 we have just been citing are perhaps not entirely con- 

 clusive; these data alone, however, offer the following 

 significant points for consideration: To account for the 

 observed sex ratios of the generic cross the maturation 

 would have to be definitely differential in (1) the elim- 

 ination of an X chromosome 5 during the spring from one 

 half of the ova, and the retention of this same X in the 

 homologous 6 eggs of the autumn. (2) The elimination 

 of a Y chromosome from the other half of the eggs laid 

 during the autumn, and the retention of all these same 

 Y's in homologous eggs of the spring; and (3) all other 

 chromosomes than the sex chromosomes must display 

 no such thing as seasonal preferences for "staying" or 

 for "going," since every observable character of the 

 hybrids betrays the presence of both of the parental 

 genera. This is not all, but let us pause at this point to 

 note that even if the sex chromosomes were here capable 

 of such wholly unknown and almost unthinkable be- 

 havior, that they have— after all— in this case wholly 

 lost the initiative in governing sex, since it is the place 

 in the season and the degree of the pressure of the over- 

 work that has been shown to prescribe the sex of the off- 

 spring; and further, the correlations of size, water con- 

 tent, energy storage, etc., which we have proved to exist 

 throughout the whole season— these correlations are all 

 established prior to the formation of even the first polar 

 body; this latter being formed only at the time of ovula- 

 tion, and the second polar body forming 1 to li hours 

 after the entrance of the egg into the oviduct. 

 If, however, we were inclined to set no bounds to the 



