230 OSCAR RIDDLE 



to list all pairs of eggs (of whatever per cent of difference in weight) 

 in which the yolks weights had been obtained and were found to 

 differ by as much as 35 per cent. This latter amount is likewise 

 abnormal for yolk weight differences; usually, this difference 

 (in pure species) is only about 9 to 15 per cent. Since the egg 

 weights of incubated eggs are thus included, the lists as given 

 contain all of the strikingly abnormal or ill-matched pairs of eggs 

 that have been encountered among the nearly 20,000 doves' eggs 

 that we have studied*. These selected data are partially classi- 

 fied in the tables (7 to 12) according to the kind of female which 

 produced the eggs. 



Several of these pairs of disproportionately sized eggs have 

 been incubated and the sex of the resulting offspring learned; 

 these data are also fully given in the tables. Sex is certainly cor- 

 related with the size, or storage metabolism, of the ova (yolks) ; 

 and, in pure species, both of these are certainly correlated with 

 the order of the egg in the clutch, as has also been pointed out in 

 earlier publications already cited. In hybrids, however, and 

 most markedly in the hybrids from the wider (generic) crosses, 

 any regularity of the presence of smaller yolks in the first eggs of 

 the clutch is lost. At the same time a high predominance of 

 males from the first and of females from the second eggs of the 

 clutch is also lost. Some instances of these conditions will be 

 observed in the tables. But, as we have previously pointed out, 

 there are conditions other than yolk size which also influence the 

 sex that is to proceed from a particular yolk. A sperm from a 

 different genus, or subfamily, may cause a male to arise from an 

 ovum which, if fertilized by its own species, would have produced 

 a female. 



Further, there is at hand considerable evidence in favor of the 

 following interpretation: The sperms formed by hybrids, par- 

 ticularly by generic, subfamily, and family hybrids, are of the 

 most varying degrees of fertilizing power. That is to say, the 

 sperms produced by a particular male vary thus, and these sperm 

 differences are probably not devoid of power to influence both 

 the degree of development and the sex of the offspring from the 

 ovum with which the sperm unites. In still other words, differ- 



