Xo. :>!).->] 



SEX CONTROL IN PIGEONS 



uration or a selective elimination of ova in the ovary? 

 This was from the first the whole of our own problem. 

 We have had no other, nor have we now, except in so 

 far as the entire question of the nature of sex— in germ 

 and adult— is concerned. 



Our method has been to study the eggs, progeny and 

 parents of such series as show this seasonal "reversal of 

 the dominance" of sex from as many different angles as 

 possible. The result till now is that we have learned 

 some ten kinds of facts concerning the germs, or the 

 prospective value of the germs, which issue from such a 

 series. Let us note that these ten lines of correlated 

 fact do not relate merely to a "normal" state of the 

 germs, but have to do with measurable changes which 

 occur when ova are subjected to the stress of parental 

 reproductive overwork, which as Whitman has shown is 

 accompanied by a shifting from male-production to 

 female-production during the progress of the season. 

 The diagrams of chart I will assist in making clear the 

 nature and significance of the several correlations. The 

 solid lines indicate a double correlation, i. e., for both 

 season and egg of clutch; the broken lines represent cor- 

 relations established thus far for only one of these. 



The generic cross that has been most fully studied in- 

 volves Turtur orien talis —the Japanese turtle dove, and 

 Streptopelia alba— the white ring dove. These species 

 together with their reciprocal hybrids are shown (photo- 

 graphed) in another chart (not given here). Some data 

 for egg size, and for sex-differences in the adult size of 

 the several forms concerned— parents and reciprocal 

 hybrids— are also given in that chart. 



The first correlation that we have established for this 

 series results from a study of the size of ova-i. e. f of 

 yolks freed from shell and albumen. The result clearly 

 establishes the fact that the yolks of late summer and 

 autumn-those that produce mostly, or all, females-are 

 larger than the yolks produced in the spring which give 

 rise to males. And there is no jump from the one size 

 to the other, but what may be better described as a 



