164 
SEXUAL selection: bikds. 
Part II. 
sion that as vocal and instrumental organs are of special 
service only to the males during their courtship, these 
organs were developed through sexual selection and 
continued use in this sex alone — the successive varia- 
tions and the effects of use having been from the first 
limited in their transmission in a greater or less degree 
to the male offspring. 
Many analogous cases could be advanced ; for in- 
stance the plumes on the head, which are generally 
longer in the male than in the female, sometimes of 
equal length in both sexes, and occasionally absent in 
the female, — these several cases sometimes occurring 
in the same group of birds. It would be difficult to 
account for a difference of this kind between the sexes 
on the principle of the female having been benefited by 
possessing a slightly shorter crest than the male, and its 
consequent diminution or complete suppression through 
natural selection. But I will take a more favourable 
case, namely, the length of the tail. The long train 
of the peacock would have been not only inconvenient 
but dangerous to the peahen during the period of incu- 
bation and whilst accompanying her young. Hence 
there is not the least a priori improbability in the 
development of her tail having been checked through 
natural selection. But the females of various phea- 
sants, which apparently are exposed on their open nests 
to as much danger as the peahen, have tails of con- 
siderable length. The females as well as the males 
of the Menura suprba have long tails, and they build 
a domed nest, which is a great anomaly in so large a 
bird. Naturalists have wondered how the female Me- 
nura could manage her tail during incubation ; but it 
been dangerous to them during incubation. He adds, that a similar 
view may possibly account for the inferiority of the female to the male 
in plumage. 
