Page:The Zoologist, 4th series, vol 2 (1898).djvu/422

390 that it has come down as a survival to the present day in a host of instances to which we have applied the explanation of "protective resemblance." The reason why it has thus survived is not because it contradicts, but because it does not require the modifying influence of natural selection. It neither broke the "law," nor did it arise through the controlling action of the "law"; and where species uninfluenced by the impulse of variation, or unharmed by a too rapid or excessive fecundity, existed in assimilative colouration to the surroundings which have remained unchanged, and subject to no climatic changes enforcing migration, such species have survived, and do appear to-day, in their original assimilative colouration.

The suggestion receives support from many facts recorded by travellers and naturalists, which, taken singly, have only the appearance of curious observations, but, considered together, exhibit more cumulative force. According to Dr. A. Leith Adams, "there is, moreover, a seemingly strong disposition for the lower parts of animals to become white in winter, i.e. the parts in closest contact with the snow; thus, the under surfaces of the Deer tribe are always whitest." Mr. J. Newton Baskett would seem to favour the same suggestion with regard to the colour of birds' eggs:—"To my mind the suggestion comes that many of our early birds with spotted eggs may have reverted from green and dead grass nesting to shingly or brilliant pebbly regions, carrying with them the bluish, greenish, creamy, or drab grounds, and by that tendency to variation for which we can never account—a thing as mysterious as life itself—they here, through the agency of natural selection, began a mottled colouradaptation which has developed so highly in our shore birds, Gulls and their relations." The well-known and much-quoted observation made by Canon Tristram in North Africa cannot be omitted here:—"In the desert, where neither trees, brushwood, nor even undulation of the surface afford the slightest protection to its foes, a modification of colour which shall be assimilated to that of the surrounding country is absolutely necessary. Hence without exception the upper plumage of every bird, whether Lark, Chat, Sylvain, or Sand Grouse, and also the fur of all the smaller