128 THE MENDEL JOURNAL 



environmental influences. In the case of the butterfly 

 caterpiflars mentioned above, certain conditions 

 associated with semi-starvation, while they do not 

 determine sex itself, do determine the proportion of 

 males and females, by unduly eliminating the latter 

 without influencing the former. But this difference 

 in the resisting powers of the two sexes is 

 probably exceptional, and, as a rule, the sexes are 

 similar in their inherent responsive powers towards 

 special environmental conditions. 



In the majority of cases, where we are in possession 

 of sufficiently accurate statistics, it appears that as a 

 general fact the sexes are produced in equal numbers. 

 This is so for Man, for the lower animals, and for 

 unisexual plants. The production of the two 

 sexes in equal numbers is a significant fact 

 from the Mendelian standpoint. It had no meaning 

 whatever in pre-Mendelian days ; but now its 

 interpretation is clear. The individual distinct- 

 ness of the sexes is also a significant fact. It 

 indicates the complete segregation of maleness 

 and femaleness. This segregation of the sexes and 

 their occurrence in equal numbers at once suggested 

 the well-known Mendehan ratio of 1:1. This ratio 

 is the result of mating a Mendelian hybrid* with an 

 individual carrying the recessive character, and it 

 indicates that one of the two sexes is a dominant 

 to the other. If we use the symbols which have 

 been previously described,* and if we tentatively 

 regard the female as a dominant hybrid and the 



* For definition and explanation see pages 63 and 67. 



