530 THE DESCENT OF MAN. 



Similar facts will hei-^after be given in regard to certain 

 herons. Young black grouse ( Tetrao tetrix) resemble the 

 young as well as the old of certain other species, for in- 

 stance, the red grouse or T. scoHcus. Finally, as Mr. 

 Blytli, who has attended closely to this subject, has well 

 remarked, the natural affinities of many species are best 

 exhibited in their immature plumage; and as the true 

 affinities of all organic beings depend on their descent from 

 a common progenitor, this remark strongly confirms the 

 belief that the immature plumage approximately shows us 

 the former or ancestral condition of the species. 



Although many young birds belonging to various fami- 

 lies thus give us a glimpse of the plumage of their remote 

 progenitors, yet there are many other birds, both dull- 

 colored and bright-colored, in which the young closely 

 resemble their parents. In such cases the young of the 

 different species cannot resemble each other more closely 

 than do the parents; nor can they strikingly resemble 

 allied forms when adult. They give us but little insight 

 into the plumage of their progenitors, excepting in so far 

 that when the young and the old are colored in the same 

 general manner throughout a whole group of species, it is 

 probable that their progenitors were similarly colored. 



We may now consider the classes of cases under which 

 the differences and resemblances between the plumage of 

 the young and the old, in both sexes or in one sex alone, 

 may be grouped. Rules of this kind were first enounced 

 by Cuvier; but with the progress of knowledge they require 

 some modification and amplification. This I have at- 

 tempted to do, as far as the extreme complexity of the 

 subject permits, from information derived from various 

 sources; but a full essay on this subject by some competent 

 ornithologist is much needed. In order to ascertain to 

 what extent each rule prevails I have tabulated the facts 

 given in four great works, namely, by Macgillivray on the 

 birds of Britain, Audubon on those of North America, 

 Jerdon on those of India, and Gould on those of Australia. 



foot-note to his translation of Cuvier's " Regne Animal," p. 159. I 

 give the case of Loxia on Mr. Blytli's information. On thrushes, see 

 also Audubon, " Ornith. Biography," vol. ii, p. 195. On Chryso- 

 coccyx and Chalcophaps, Blyth, as quoted in Jerdon's "Birds of 

 India." vol. iii, p. 485. On Sarkidiornis, Blyth, in "Ibis," 1867, p, 

 175. 



