Jhai'. XVI. Birds — Young like both Adults. 483 



were not albinoes, as shewn by the colour jf their beaks uud legs, whii b 

 aeai'ly reoembleJ the same parts in the adults.^'' 



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 

 resi mble each other, liy the curious case of the gtniis I'asser.^' In the 

 house-sparrow (P. domesficusj the male (lifters much from the female 

 and from the young. '1 he jouiig and the females are alike, and 

 resemble to a large extent both sexes and the voung of the sparrow (il 

 Palestine (P. brachydactylus), as well as uf some allied species. VVi 

 may therefore assume tliat the female and young of the house-sparrow 

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

 Now with the tree-spanow (P. montanus) both sexes and the joun^ 

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

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

 colouring of their early progenitor. This may have b.'cn effected by 

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

 mature ; or, secondly, whilst quite young, and by havin>i; in either case 

 transmitted his movlified plumage fo 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 

 prevailed throughout the present class of cases. That the males varied 

 whilst young, and transmitted their variations to tneir offspring of both 

 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 oeourring 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 flist,'* second, and fourth 

 classes of cases ; but they fail in the third, often in the fifth,^* 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 geiier'aliaatiou by Dr. W. Marshall with respect to the protu- 

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



'^ ' Bulletin de la Soc. Vaudoise Audubon, ' Ornlth. Biography,' vol. 



des So. Nat.' vol. x. 1869, p. 182. i p. 233, 280,378.) The Harlequin 



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



Cygnus immutdbilis 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 



dor), his full splendour until the end of 



" I am indebted to Mr. Blyth the September m the following 



for information in regard to this year. 



genus. The sparrow of Palestine '* Thus the Ibis tantalus and Graa 



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



^' For instance, the males of Flamingo several years, and the 



Tanagra cBstiva and Fringilla cyanca Ardea ludovicana two years, before 



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



Frim/iUa ciris (bur years, to con- See Audubon, ibid. vol. i. p 221 | 



plete 'heir lieautifnl plumage. (See vol. iii. pp. 133, 139, 211. 



