Chap. XVI.] INHERITANCE, LIMITED BY AGE. 175 



CHAPTER XVI. 



Birds — concluded. 



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

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

 between the Males of Closely-allied or Eepresentative 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. 



We must now consider the transmission of characters 

 as limited by age in reference to sexual selection. The 

 truth and importance of the principle of inheritance at 

 corresponding ages need not here be discussed, as enough 

 has already been said on the subject. Before giving the 

 several rather complex rules or classes of cases, under 

 which all the differences in plumage between the young 

 and the old, as far as known to me, may be included, it 

 will be well to make a few preliminary remarks. 



With animals of all kinds, when the young differ in 

 color from the adults, and the colors of the former are 

 not, as far as we can see, of any special service, they may 

 generally be attributed, like various embryological struct- 

 ures, to the retention by the young of the character of an 

 early progenitor. But this view can be maintained witli 

 confidence only when the young of several species closely 

 resemble each other, and likewise resemble other adult 

 species belonging to the same group ; for the latter are 

 the living proofs that such a state of things was formerly 



