The Determination of Sex 365 
Diecious 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 
tule is far from invariable. 
In regard to the human race, statistics from the whole of 
Europe, including records of ‘“‘millions” of births, show that 
for every 100 female children born there are 106 males. If a 
more limited range is taken, or a shorter period, some devia- 
tions from this proportion are found. 
Thus between the years 1887-1895 the following ratio of the 
sexes to each other is given by Bodio: — 
MALES 
Italy. , : 5 ‘ ‘ : 105.8 
France P 5 : - ‘ . . 104.6 
England. . . ; . : ‘ 103.6 
Germany . ‘ : : 3 i ; 105.2 
Austria j ‘ ; s ‘é : : 105.8 
Hungary. ‘ ; : : ‘ . 105.0 to 100 females 
Switzerland . : é 2 : ‘ é 104.5 
Belgium ; : F ‘ 2 : 104.5 
Holland 3 é . 7 : 3 i 105 5 
Spain . F é . : 5 é 108 3 
Russia : é F 3 5 é ‘ 105.4 J 
