world--Protective colouring--Conspicuously coloured birds--Novelty
appreciated--Summary of the four chapters on birds.


CHAPTER XVII.

Secondary Sexual Characters of Mammals.

The law of battle--Special weapons, confined to the males--Cause of absence
of weapons in the female--Weapons common to both sexes, yet primarily
acquired by the male--Other uses of such weapons--Their high importance--
Greater size of the male--Means of defence--On the preference shewn by
either sex in the pairing of quadrupeds.


CHAPTER XVIII.

Secondary Sexual Characters of Mammals--continued.

Voice--Remarkable sexual peculiarities in seals--Odour--Development of the
hair--Colour of the hair and skin--Anomalous case of the female being more
ornamented than the male--Colour and ornaments due to sexual selection--
Colour acquired for the sake of protection--Colour, though common to both
sexes, often due to sexual selection--On the disappearance of spots and
stripes in adult quadrupeds--On the colours and ornaments of the
Quadrumana--Summary.


PART III. SEXUAL SELECTION IN RELATION TO MAN, AND CONCLUSION.