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Rh feathers is regulated by the regions in which they live, the tendency to melanism being chiefly noticeable in the southern hemisphere, and particularly in New Zealand, Madagascar, and New Guinea. The Swan furnishes a marked example of this, as its white plumage of the northern hemisphere becomes of a pure raven hue in Australia; while in Terra del Fuego and the adjacent portions of South America some of the wing-feathers only are black; and in Chili the head and neck are alike jet, the remainder of the body remaining snow-white. This is again visible in the Perroquets in New Zealand, their plumage showing only small portions of bright red and yellow, and the rest being of a dingy green, deepening into black; while the same species in those islands of the Pacific near Africa display similar signs. In Madagascar and the Mauritius, the Seychelles and the Comoro Islands, black Parrots are frequently met with. Other examples, such as Ducks, Kingfishers, &c., can be easily quoted; and it has been found that, in the Southern IndoPacific region, those birds which elsewhere present the most brilliant colours are either there darkened to black or fade away to white."

New Zealand presents many examples of the latter; and Dr. Buller mentions its occurrence in eleven species. Difference of colour, produced by climatic change, is a long subject. We can always tell a bird which has just landed at Brighton from one of the same kind which has passed the winter here, from the superior freshness and brightness of its colours. I have examples in my own collection to show this distinction. It is an interesting topic, on which I could be tempted to run off, but must not. I may, however, mention that there are several ways by which changes in the appearance of the plumage of birds may be produced. Owen gives them as follows:—"By the feather itself becoming altered in colour; by the birds obtaining a certain number of new feathers without shedding any of the old ones; by the wearing off of the lengthened lighter-coloured tips of the barbs of the feathers on the body, by which the brighter tints of the plumage underneath are exposed; by an entire or partial moulting, at which old feathers are thrown off and new ones produced in their places. The first