300 
THE PRINCIPLES OF 
Part II. 
In the following chapters, I shall treat of the 
secondary sexual characters in animals of all classes, 
and shall endeavour in each case to apply the prin- 
ciples explained in the present chapter. The lowest 
classes will detain us for a very short time, but the 
higher animals, especially birds, must be treated at 
considerable length. It should be borne in mind that 
for reasons already assigned, I intend to give only a few 
illustrative instances of the innumerable structures by 
the aid of which the male finds the female, or, when 
found, holds her. On the other hand, all structures 
and instincts by which the male conquers other males, 
and by which he allures or excites the female, will be 
fully discussed, as these are in many ways the most 
interesting. 
Supplement on the proportional numbers of the two sexes 
in animals belonging to various classes. 
As no one, as far as I can discover, has paid atten- 
tion to the relative numbers of the two sexes through- 
out the animal kingdom, I will here give such materials 
as I have been able to collect, although they are ex- 
tremely imperfect. They consist in only a few instances 
of actual enumeration, and the numbers are not very 
large. As the proportions are known with certainty on 
a large scale in the case of man alone, I will first give 
them, as a standard of comparison. 
Man. — In England during ten years (from 1857 to 
1866) 707,120 children on an annual average have 
been born alive, in the proportion of 104*5 males to 
100 females. But in 1857 the male births through- 
out England were as 105 # 2, and in 1865 as 104*0 to 
100. Looking to separate districts, in Buckinghamshire 
(where on an average 5000 children are annually born) 
