The Determinatio7i of Sex 



365 



Dioecious Species, composed of Unisexual Individuals 



When the species consists of male and female individuals, we 

 find in some cases that the sexes are so much alike externally, that 

 without a knowledge of their internal structure we could not tell 

 them apart. Some birds, pigeons, for example, belong to this 

 class, and there are even some mammals, mice for instance, 

 in which the sexes are so closely similar that an inspection of the 

 external organs of reproduction is necessary to reveal the sex. 

 In many other cases the external differences involve mainly 

 the external organs of reproduction, while in still other groups 

 the whole form of the body may be different, and in extreme 

 cases this difference is so great- that were not the relation of 

 the individuals known they would be placed in different 

 species. 



Where the sexes are separate it may be said to be the rule 

 for equal numbers of males and females to exist, but this 

 rule is far from invariable. 



In regard to the human race, statistics from the whole of 

 Europe, including records of "milhons" of births, show that 

 for every 100 female children born there are 106 males. If a 

 more hmited range is taken, or a shorter period, some devia- 

 tions from this proportion are found. 



Thus between the years 1 887-1 895 the following ratio of the 

 . sexes to each other is given by Bodio : — 



Italy . 



France 



England 



Germany 



Austria 



Hungary 



Switzerland 



Belgium 



Holland 



Spain . 



Russia 



Males 

 105.8 

 104.6 

 103.6 

 105.2 

 105.8 

 105.0 

 104.5 

 104.5 



I05-5 

 108.3 

 105.4 



to 100 females 



