486 The Descent of Man. Part 11, 



resemble the adults, firstlj', in their winter dress; secnndly, and this '\» 

 of muuh rarer occurrence, in their summer dre^s; thirdly, tliey may bi' 

 iiiternifdiate between these two states; and, fourthly, they luay differ 

 greatly from the adults at dU seasons. We have an instance of the 

 (irot of these four cas, s in one of the egrets of India {Buphus c-oru- 

 mandus), in which the young and the adults of both sexes are wliito 

 during the winter, the aduUs becoming tjoldeu-buff during thr suiniuer. 

 With ^he naper [Anastomus oscitans) of India we have a Hmilai- rabe, 

 but the colours are reversed: for the young and tne adults of bntli 

 sexes are grey and black during the winter, the adults becoming white 

 during the summer." As an instance of the second case, the y>iuiig oi 

 the rnzor-bill {Alca tarda, Linn.), in an early state of plumage, are 

 coloured like the adults during the summer; and the young of tJie 

 white-crowned sparrow of North America {Fringilla leuanphrys), as soon 

 as fledged, have elegant white stripes on their heads, which are lost by 

 the young and the old during the winter.*' With respect t.i the third 

 case, namely, that of the young having an intermediate character between 

 the summer and winter adult plumages, Yarrell" insists that this 

 occurs wilh many waders. Lastly, in reginl to the young ditfering 

 greatly from both sexes in theii' adult summer and winter plumages, 

 this occurs with some herons and egrets of Noith America and India, — 

 the young alone being white. 



I will make only a few remarks on these complicated cases. When 

 the young resemble tiie females in their sumnier dress, or the adults of 

 bdth sexes in their winter dress, the cases diti. r from those given under 

 Classes I. and III. only in the characters originally acquired by the 

 males during the breeding-season, haviug been lim ted in their trans- 

 mission to the corresponding season. Wiien thi' adults have a distinct 

 summer and winter plumage, and the yoirag differ from both, the care 

 is more difficult to iLiiclerstand. We may admit as probable that the 

 young have retained an ancient state of plumage ; we can account by 

 sexual selection for the summer or nuptial plumage of the adults, but 

 how are we to account for their distinct wilder plumage? If we couid 

 admit that this plumage serves in all cases as a jirotection, its ac- 

 quirement would be a simple affair; but there seems no good reason 

 for this admission. It may be suggested that the widely ditl'erent 

 conditions of life during the winter and summer have acted in a direct 

 manner on the plun.age; this m.iy have had some eft'ect, but I have 

 not much confidence in so great a difference as we sometimes see 

 between the two plumages, having been thus caused. A more probuble 

 explanation is, that an ancient style of plumage, paitially modified 

 through the transference of some characters from the summer plumag.t, 

 has been retained by the adults during the winter. Finally, all ihe 

 easiss in our present class apparently depend on characters acquired hy 

 the adult males, having been variously limited in thiir trauomissum 

 according to age, season, and sex; but it would not lie worth while lu 

 attempt to follow out these crmplox relations. 



" I am indebted to Mr, Klyth On the Fringilla kucophr^s, Au- 



for information as to the Buphuy; dubon, ibid. vol. ii. [>, 89. I shall 



see also Jerdo"!, * Birds of Indiii,' hiive hereafter to refer to the young 



vol. iii. p. 749. On the Anastomus, of certaiQ herons and egrets being 



Bee Blyth, in 'Ibis,' 1867, p. 173, white, 



"'•' On the Alca, see Macgillivray, " ' Historv of Bi itisli Binls,' vol 



IJi^t, Brit, Birds,' yA. y. p, 3+7. i. 1839, p, 159 



