We must ascribe to the influence of the processes of selection the exact regulation of the duration of the winter and summer dress, which has been carefully studied in the case of the variable hare. In the high Alps it remains white for six or seven months, in the south of Norway for eight months, in Northern Norway for nine months, and in Northern Greenland it never loses its white coat at all, as there the snow, even in summer, melts only in some places and for a short time. But apart from concealment there is certainly another adaptation involved here--namely, the growth of the hair as a protection against the cold. From an old experiment made in 1835 by Captain J. Ross, and recently brought to light again by Poulton, we learn that a captive lemming kept in a room in winter did not change colour until it was exposed to the cold. The constitution of animals which become white in winter is thus so organized that the setting in of cold weather acts as a stimulus which incites the skin to the production of white hairs. This predisposition also we must refer to the influence of natural selection, since it must have been very useful to the species that the winter coat should grow just when it was necessary as a protection against cold. This explains at the same time why the predisposition to respond to the stimulus of cold by a growth of winter fur finds expression earlier in those colonies of Arctic animals, such as the hare, which live in Lapland, than in those which live in the south of Norway. But that it is not the _direct_ influence of cold which colours the hair of a furred animal white we can see from our common hare (_Lepus timidus_), which, in spite of the winter's cold, does not become white, but retains its brown coat, and not less so from the mountain hare (_Lepus variabilis_), which in the south of Sweden also remains brown, although the winter there may be exceedingly cold. But as the covering of the ground with snow is not so uninterrupted there as in the higher North, a white coat would be not a better protection than a brown one, but a worse. The white colouring of Arctic animals is therefore not directly due to the influence of the climate, as has often been maintained, but is due to it indirectly, that is, through the operation of natural selection. I have tried to make this clear by means of this example, so that we may not have to repeat it in considering those which are to follow. * * * * * But all attempts at any other explanation are even more decidedly excluded when we turn our attention to more complicated cases of colour-adaptation, which are not confined to the simple, general coloration, but are helped by markings and colour-patterns, that is, by schemes of colour. Thus numerous caterpillars exhibit definite lines and spots on their ground-colouring, which, in one way or another, aid in protecting them from their enemies.