Chap. XVI. INHERITANCE, LIMITED BY AGE. 183 



CHAPTEE XYL 



Birds — concluded. 



The immature plumage in relation to the character of the plumage 

 in both sexes when adult — Six classes of cases — Sexual differ- 

 ences 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 iu the Birds of the World — 

 Protective colouring — Conspicuously-coloured 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 inheri- 

 tance 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 

 colour from the adults, and the colours of the former are 

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

 may generally be attributed, like various embryological 

 structures, to the retention by the young of the character 

 of an early progenitor. But this view can be maintained 

 with 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 possible. Young lions and pumas 



