Xo. •>!).")] 



SEX CONTROL IN PIGEONS 



3S7 



tably— a profound modification of the sex-ratio, and iden- 

 tified in a general way the factors associated with the 

 modified ratios. Whether the modified ratios signified a 

 real control— a reversal— of sex could not at that time 

 be definitely decided. It was to help in making a deci- 

 sion as to whether the changed sex-ratios signified a 

 real— or only an apparent— reversal of sex that I pro- 

 posed in the winter of 1908-9 to carry out some chem- 

 ical studies on the ova of the doves and pigeons which in 

 Whitman's hands were yielding these striking sex ratios. 

 The methods for the quantitative and qualitative anal- 

 ysis, of the very small samples to be used, were devel- 

 oped, and these were tested during 1909-10 on consider- 

 able numbers of the larger ova of jungle fowls and do- 

 mestic fowls. Since April, 1911, I have carried on this 

 and other lines of study to determine if possible whether 

 the changed ratios observed by Whitman involve a real 

 reversal of sex ; this work is being actively continued. 



Whitman showed that " width of cross" in doves and 

 pigeons is of first importance in determining sex ratios 

 and that the wider the cross the higher is the proportion 

 of males. Family crosses produce— in practically all 

 matings— only male offspring. Generic crosses produce 

 from their " stronger" germs— those of spring and early 

 summer— nearly all males. If, however, the birds of 

 such a generic cross be made to 1 'overwork at egg-pro- 

 duction"— that is if their eggs are taken from them as 

 soon as laid and given to other birds for incubation- 

 then the same parents which in the spring threw all or 

 nearly all male offspring may be made to produce all, 

 or nearly all, female offspring in late summer and 

 autumn. At the extreme end of the season eggs capable 

 of little, then of no development, are often found in such 

 a series. As the birds of such a mating grow older the 

 time of appearance of females, and of eggs incapable of 

 full development, is reached earlier and earlier in the 

 summer or spring. 



In the case of a number of hybrids Whitman showed 

 that color is also affected by this pressure of reproduc- 



