iv CONTEXTS. 



Birds. — Variations sometimes abrupt. — Laws of Variation. — Formation 

 of Ocelli. — Gradations of Character. — Case of Peacock, Argus Pheas- 

 ant, and Urosticte . . . . . . . p. 95 



CHAPTER XV. 



BIRDS — contiimed. 



Discussion why the Males alone of some Species, and both Sexes of other 

 Species, are brightly colored. — On Sexually-limited Inheritance, as ap- 

 plied to Various Structures and to Brightly-colored Plumage. — Nidifi- 

 cation in Relation to Color. — Loss of Nuptial Plumage during the 

 Winter ........ 147 



CHAPTER XVI. 



B I R DS — concluded. 



The Immature Plumage in Relation to the Character of the Plumage in 

 both Sexes when Adult. — Six Classes of Cases. — Sexual Differences 

 between the Males of Closely-allied or Representative Species. — The 

 Female assuming the Characters of the Male. — Plumage of the Young 

 in Relation to the Summer and Winter Plumage of the Adults. — On 

 the Increase of Beauty in the Birds of the World. — Protective Color- 

 ing. — Conspicuously-colored Birds. — Novelty appreciated. — Summary 

 of the Four Chapters on Birds ..... 175 



CHAPTER XVII. 



SECONDARY SEXDAL 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 Weap- 

 ons. — Their High Importance. — Greater Size of the Alale. — Means of 

 Defence. — On the Preference shown by either Sex in the Pairing of 

 Quadrupeds ....... 228 



CHAPTER XVIII. 



SECONDARY SEXUAL CHARACTERS OF MAMMALS Continued. 



Voice. — ^Remarkable Sexual Peculiarities in Seals. — Odor. — Development 

 of the Hair. — Color of the Hair and Skin. — Anomalous Case of the 

 Female being more ornamented than the Male. — Color and Ornaments 

 due to Sexual Selection. — Color acquired for the Sake of Protection. — 

 Color, though common to both Sexes, often due to Sexual Selection. — 



