SPECIAL CASES OF SEX-INHERITANCE 227 



Pearl has recently pointed out that the sex ratio 

 in the Argentine Republic varies somewhat accord- 

 ing to whether individuals of the same race, or of dif- 

 ferent races, are the parents. As seen in the following 

 table, the sex ratio of Italian by Italian is 100.77; 



COMPARISON OF THE SEX RATIOS OF THE OFFSPRING OF PURE AND 

 CROSS MATINGS 



Argentine by Argentine, 103.26 ; but Italian by Argen- 

 tine, 105.72. If, as has so often been found to be the 

 case, a hybrid combination gives a more vigorous 

 progeny, the higher sex ratio of the cross-breed may 

 account for the observed differences, since other data 

 show that the male infant is less viable and the in- 

 creased vigor of a hybrid combination may increase 

 the chance of survival of the male. 



