20 STATISTICS OF SEX 



To compare the statistics I have collected the sexes of triplets found 

 in the French and German tables of births with the following results : 



France Berlin T , , 



1858-1900 1853-1880 



3 males 342 32 374 



3 females 304 28 332 



Total unisexual 646 60 706 



Bisexual 667 43 710 



Observed proportion of unisexual triplets 49.9 per cent. 



It appears from these numbers that when we compare the probabilities 

 derived from the case of twins with the actual facts in the case of triplets, 

 there is a discrepancy. From the facts in the case of twins, we should 

 conclude that 46.9 per cent of all triplets should be unisexual; we actu- 

 ally find that 49.9 per cent is unisexual, an excess of 3 per cent. 



The discrepancy may take the other form by determining the amount of 

 unisexual preponderance in the case of triplets as we have done in the 

 case of twins. This preponderance is 0.79 instead of 0.77. That is to 

 say, grouping the triplets as we have the twins, there is a probability of 

 0.79 that any one organism of a triplet of group A will develop into a 

 male, and that one of group B will develop into a female. The coefficient 

 of unisexual tendency is, therefore, for triplets, 



a = 0.29 



Now, we should suppose, a priori, that the ratio of the unisexual pre- 

 ponderance to the effects of the accidental causes which finally determine 

 the sex would be the same with twins and triplets. It is true that the 

 discrepancy between 0.27 and 0.29, or between 46.9 and 49.9 per cent is 

 not greater than might easily have been the result of fortuitous deviation. 

 Still it is larger than we should expect. If we may regard it as expressing 

 a real law, we may suppose that, besides the independent causes at action 

 tending toward one sex or the other, there is an interaction between the 

 two organisms, by which the sex of one influences that of the other in 

 its own direction. 



Apart from this, the general conclusions from triplets confirm that 

 from twins -)- there are not male and female germs. It would seem 

 that we have in this a practical!}' conclusive negation of the theory of 

 completely determined sex in the original germs and may provisionally 

 accept that of complete asexuality on the part of such germs, subject, 

 however, to farther statistical tests. 



