ICS 



THE AMERICAN NATURALIST 



[Vol. L 



of animals may possibly be explained. A species such as 

 man, which constantly seems to produce more males than 

 females, may be said to form more active or vigorous 

 male-producing spermatozoa. In the competition to fer- 

 tilize the egg such spermatozoa win an advantage and in 

 the sum total more males than females arise, the ratio 

 depending upon the extent of the advantage the one class 

 of spermatozoa has over the other. 



We now have under way a number of matings which 

 are designed to test these propositions in an analytical 

 fashion. One of us (Papanicolaou, '15) is in possession 

 of data giving reason to believe that a second explanation 

 may be offered to account for the different conditions pre- 

 sented by the male and female offspring produced by alco- 

 holized females. Such an explanation is based on the 

 supposition that the female guinea pig as well as the male 

 has a share in the determination of the sex ratio and may 

 produce two kinds of ova. Such an explanation in its 

 final analysis is extremely complex and unnecessary in 

 the present discussion, though it will be presented in a 

 future consideration of the regulation of the sex ratio in 

 these animals. 



Admitting, as is suggested above, that the two groups 

 of spermatozoa differ in their response and resistance to 

 the treatment, we may also admit that there are other 

 normal differences in their vitality and behavior. These 

 normal differences must also vary within certain limits. 

 In one group of animals the female-producing sperma- 

 tozoa may be more active and possess a higher degree of 

 fertilizing power than the male-producing spermatozoa. 

 Such a group would show a sex ratio below one hundred, 

 there being more females than males produced. In other 

 species of animals with a sex ratio of more than 100 the 

 reverse condition obtains; the male-producing sperma- 

 tozoa possess on an average a higher fertilizing power 

 than the female-producing. But the advantage of the 

 male-producing sperm may be slight and no doubt many 

 individual males tend to form female-producing sperm 



