;hai\ XVI. Birds — Young like both Adults. 483 



were not albinoes, as shewn by the colour ~>i their beaks and legs, which 

 nearly resembled the same parts in the adults. 3 '-' 



It may be worth while to illustrate the above three modes by which, 

 in the present class, the two sexes and the young may have come to 

 resemble each other, by the curious case of the genus Passer. 33 In the 

 house-sparrow (P. domesticus) the male differs much from the female 

 and from the youug. The young and the females are alike, and 

 resemble to a large extent both sexes and the young of the sparrow of 

 Palestine (P. brachydactylus), as well as of some allied species. We 

 .uiay therefore assume that the female and young of the house-sparrow 

 approximately shew us the plumage of the progenitor of the genus. 

 Now with the tree-sparrow (P. montanus) both sexes and the joung 

 closely resemble the male of the house-sparrow; so that they have all 

 been modified in the same manner, and all depart from the typical 

 colouring of their early progenitor. This may have been effected by 

 a male ancestor of the tree-sparrow having raried, firstly, wnen nearly 

 mature ; or, secondly, whilst quite young, and by having in either case 

 transmitted hid mo dried plumage to the females and the young; or, 

 thirdly, he may have varied when adult and transmitted his plumage 

 to both adult sexes, and, owing to the failure of the law of inheritance 

 at corresponding ages, at some subsequent period to his young. 



It is impossible to decide which of these three modes has generally 

 pr- vailed throughout the present class of cases. That the males varied 

 whilst young, and transmitted their variations to their offspring of bolh 

 sexes, is the most probable. I may here add that I have, with little 

 success, endeavoured, by consulting various works, to decide how far 

 the period of variation in birds has generally determined the transmis- 

 sion of characters to one sex or to both. The two rules, often referred 

 to (namely, that variations occurring late in life are transmitted to one 

 and the same sex, whilst those which occur early in life are transmitted 

 to both sexes), apparently hold good in the first, 34 second, and fourth 

 classes of cases ; but they fail in the third, often in the fifth, 35 and in 

 the sixth small class. They apply, however, as far as 1 can judge, to 

 a considerable majority of the species; and we must not forget the 

 striking generalisation by Dr. W. Marshall with respect to the protu- 

 berances on the heads of birds. Whether or not the two rules generally 



32 ' Bulletin de la Soc. Vaudoise Audubon, ' Ornith. Biography,' vol, 

 des Sc. Nat.' vol. x. 1869, p. 132. i p. 233, 280, 378.) The Harlequin 

 The young of the Polish swan duck takes three years (ibid. vol. iii. 

 Cygnus immutabilis of Yarrell, are p. 614). The male of the Gold 

 always white ; but this species, as pheasant, as I hear from Mr. 

 Mr. Sclater informs me, is believed Jenner Weir, can be distinguished 

 to be nothing more than a variety from the female when about three 

 of the domestic swan (Cygnus months old, but he does not acquire 

 olor). his full splendour until the end of 



33 I am indebted to Mr. Blyth the September in the following 

 for information in regard to this year. 



genus. The sparrow of Palestine 35 Thus the Ibis tantalus and Grus 



belongs to the sub-genus Petronia. americanus take four years, the 



34 For instance, the males of Flamingo several years, and the 

 Tanagra a:siiva and Fringilla cyanca Ardea ludovi.ana two years, before 

 require three years, the male of they acquire their perfect plumage. 

 Fringilla ciris four years, to con- See Audubon, ibid. vol. i. p 221 j 

 piste their beautiful plumage. (See vol. iii. pp. 133, 139, 211. 



