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Show 178 SEXUAL Sl!:LECTION: BIRDS. PART IL great number of breeds and sub>-breeds, and in .those tho sexes generally differ in plu~age; so that It h~s b een no tI.C e d 'a s a r·emarkablo· circumstance· when hme certain sub-breeds tboy resemble each. oth~r. On t other hand, the domestic pigeon has likewise produce~ a vast number of distinct breeds and sub-bree~s,. an~ in these, with rare exceptions, the tw~ sexes are Identically alike. Therefore if other spe.Cies. of Gallus and Columba were domesticat.ed and vaned, It would not be rash to predict that the same gen~ral rules of sexual similarity and dissimilarity, depenclmg on the form of transmission, would, in both cases, ho!d. good.. In a similar maner the same form of transmission has generally prevailed througl~out the ~arne natural gr~u~s; although marked except10ns to this rule occur. Withm the same family or even genus, the sexes may be identically alike or very different in colour. Instances have already been given relating to the same genus~ as with sparrows, fly-catchers, thrushes and grouse. In tho family of pheasants the male~ ~n~ females of alm~st all tho species are wonderfully dissimilar, but are qmte similar in the eared pheasant or Orossoptilon auritum. In two species of Chloohaga, a genus of geese, the· males cannot be distinguished' from the females, exc~pt bv size· whilst in two others, the sexes are so unhke tl~at the~ might easily be mistaken for distinct species.28 The laws of inheritance can alone account for the following cases, in which the female by acquiring at a late period of life certain character:s ~roper to the male, ultimately comes to resemble him m a more or less complete manner. Here prote~tion can hardly have come into play. Mr. Blyth mforms- me that the females of Oriolus melanocephalus ancl 0f some· 2s The 'Ibis/ ' vol. vi. 186-1, p. 122. CHAP. XV. COLOUR AND NIDIFICATION. 179 allied species, when sufficiently mature to breed, differ considerably in plumage from the adult males ; but after the second or third moults they differ only in their beaks having a slight greenish tinge. In the dwarf bitterns (Ardetta), according to the same authority, " the male acquires his final livery at the ''first moult, the female not before the third or fourth " moult; in the meanwhile she presents an inter" mediate garb, which is ultimately exchanged for the " same livery as that of the male." So again the female Falco peregrinus acquires her blue plumage more slowly than the male. Mr. Swinhoe states that with one of the Drongo shrikes (Dicrurus macrocercus) the male whilst almost a nestling, moults his soft brow~ plumage and becomes of a uniform glossy greemsh-black; but the female retains for a Ion()' time the white strire and spots on the axillary feathers; and does not completely assume the uniform black colour of the male for the first three years. The same excellent observer remarks .that in the spring of the second year the female spoonbill (PJatalea) of China re~ e~bles the male of the first year, and that apparently It IS not until the third spring that she acquil'Cs the same adult plumage as that possessed by the male at a ~uch earlier age. The female Bombycilla carolinensis clrf~'ers ;ery little from the male, but the appendages, which hke beads of reel sealing-wax ornament the wjngfeathers, are not developed in her so early in life as in the male. The upper mandible in the male of an Indian parrakeet (Palt£ornis Javanicus) is coral-red from his · earliest youth, but in the female, as Mr. Blyth has , observed with caged and wild birds, it is at first black and does not become reel until the bird js at least a year , old, at . which ag~ the sexes resemble each other in all respects. Both sexes 'of the wild turkey are ultimately N 2 |