MODIFICATION OF THE GERM-CELLS IN MAMMALS 213 



the'behavior of the X and Y groups of spermatozoa is the ingenious 

 double-mating experiment of Cole and Davis (14) with rab- 

 bits. They found that when two male rabbits were mated with 

 a single female, superfetation occurred in most cases, so that 

 part of the resulting litter of young were sired by one male and 

 part by the other. The males differed in their fertilizing abili- 

 ties, so that one more often sired the majority of young of a 

 given litter, and in the total number of competition matings he 

 sired the greater number of young. This male with the fertiliz- 

 ing advantage was then treated for a month or more with the 

 fumes of alcohol by the inhalation method. As a result of this 

 treatment his spermatozoa became affected in such a way that 

 mated in competition with the same male he normally had 

 beaten he now^ failed to sire any young. Yet when mated singly 

 or alone with a female he still possessed the power to beget off- 

 spring. This is a striking illustration of the debilitating effect 

 of a short alcohol treatment on the physiological behavior of 

 these spermatozoa, thus lowering their fertilizing ability below 

 that of other spermatozoa which were formerly less potent than 

 they. 



When it is seen how definitely and readily alcohol treatments 

 affect the behavior of the spermatozoa, we are led to speculate as 

 to whether the treatment might not affect the X and Y groups 

 of sperm differently, and thus be partially responsible for a dis- 

 tortion of the sex-ratios, should such occur. This responsibility 

 may be due in the first place to a lowered fertilizing power on 

 the part of one group of spermatozoa, thus giving rise to fewer 

 individuals of one sex than of the other. Or, in the second 

 place, even though both groups of spermatozoa should be equally 

 capable of fertilizing the eggs, one group might be more affected 

 as to its ability to produce viable zygotes in combination with 

 normal ova, and thus an early differential sex mortality would 

 occur causing a modification of the proportion of one sex to the 

 other among the young born. We have elaborated somewhat on 

 these possibilities in the section devoted to the sex-ratios of the 

 alcoholic guinea-pigs. 



Cole and Davis originally devised their experiment as a cru- 



