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Show DARWINISM CIIAl'. both inconsistent with any other theory than that the whito colour of arctic animals has been acquired for concealment, and to that theory both afford a strong support. Here wo have a striking example of the exception proving the rule. In the desert regions of the earth we find an even more general accordance of colour with surroundings. The lion, the cmuel, and all the desert antelopes have more or le. s the colour of the sa.nd or rock among which they live. Th' Egyptian cat and the Pampas cat are sandy or earth coloured. The Australian kmgaroos arc of similar tints, and the origiwtJ colour of tho wild horse is supposed to have hcen sanely or clay coloured. Birds arc equally well protected by assimilative hues; tho la.rks, quails, goatsnckcrs, a.nd grouse which abonnd in tho North Afri an and Asiatic deserts are a.ll tinted or mottled so as closely to rosem blc tho avera.gc colour of the soil in tho eli tricts they inhabit. Canon Tri.->tmm, who knows these rcgion:o; and their natural hi story so well, says, in an often quoted passage: "In the desert, where neither trees, brush wood, nor even undulatioll.' c,f the . urfaco afford the slightest protection to its focR, a modification of colour which shall be assimilated to that of the surrounding country is absolutely ncce. sary. IJ ·nco, without exception, the upper plumage of every bird, whether lark, chat, . ylvain, or sand-grouse, and also the fur of all the smaller mamma.ls, and the skin of all the snakes and lizard. , is of one uniform isabelline or sand colour." Pas ing on to the tropical regions, it is among their evergreen forests alone that we find whole groups of hil'(lK whose ground colour is green. Parrots arc very rYcncmlly green, and in the East we have an extensive group of gn'<'ll £mit-eating pigeons; while the barbots, boo -caters, tnracoK, leaf-thrushes (Phyllornis), white-eyes (Zo. tcrops), and Jll any other groups, have so much green in their plumage as to ten<l greatly to their concealment among the dense foliage. Thoro can be no doubt that the. o colours have been acquired a~ a protection, when we see that in all the temperate regions, where the leaves are deciduous, the ground colour of tho great majority of birds, especially on tho upper surface, is :t rusty brown of various shades, well corre. pondi11g with the bark, withered leaves, ferns, and bare thickets among whi·eh VII[ ORIGIN AND U E OF OLOUR IN ANIMAL. 193 they live in autumn and winter, and especially in early spring when so many of them build their nests. N oeturnal animals supply another illustration of the same rule, in the dn ky colour. of n1icc, rats, bats, and moles, and in tho soft mottled plumage of owl. and goatsnckers which, while almost equally inconspicuous in the twilight, are such as to favour their concealment in the daytime. An additional illustration of general assimilation of colour to tho surroundings of animalR, j, furni shed by the inhabitants of the deep oceans. Profcs:or Moseley of the Challenger Expedition, in his Briti ~h As:ociation lecture on this subject, says : "Most characteristic of pelagic animals is the almost crystalline tra.n. parency of their bodies. So perfect i. thi. transparency tha.t very many of them arc rendered almost entirely in vi. ihle when floating in the water, while some, even when caught and held np in a gla. s globe, are hardly to be seen. The skin, nerves, muscles, a.nd other organs arc ab. olutoly hyaline and transparent, bnt the liver and dige:tivc tract often remain opaqne and of a yellow or brown colom, and exactly resemble when Recn in the water small pieces of floating seaweed." Such marine organi. ms, however, as are of larger size, and either occasionally or habitually float on the surface, arc beautifnlly tinged with blue ahove, thns hn.rmoni ing with the colonr of the . ea as cen by hovering birds; while they are white below, and arc thu. invi. ihle against the wave-foam and clouds as seen by enemies beneath the surface. Such are the tints of the beautiful nudibranchiate mollu. c, G laucus atlanticus, and many others. Geneml Them·1ps of Animal Colmtr. We are now in a position to test the general theories, or, to speak more correctly, the popular notions, as to the origin of animal coloration, before proceeding to apply the principle of utility to tho explanation of some among the many extraordinary manifestations of colour in the animal world. The most generally received theory undoubtedly is, that brilliancy and variety of colour are due to the direct action of light and heat; a theory no doubt derived from the abundance of bright - coloured birds, insects, and flowers which arc brought from tropical regions. There arc, however, 0 |