Page:The Zoologist, 4th series, vol 5 (1901).djvu/269

Rh must be very different. The tail as a balancer must be as much required in summer as in winter, if not more so; but, on the other hand, the tail as a warm covering is not so necessary, and hence probably the reason of its not being renewed. There is, however, a further noticeable point about this tail, which is fully dealt with by Mr. Thomas in the article quoted above, and that is, that as it gets older it becomes lighter in colour, till by autumn it is nearly white. Mr. Thomas further points out that the red hairs of summer show no tendency to this bleaching process, whilst the brown winter hairs slowly bleach throughout the time they are worn, but, being replaced in spring, the process is never so conspicuous on the body as on the tail, where the change goes on throughout the year.

Although we are accustomed to see fur and feathers of all kinds "bleach" under the action of light, we are perhaps too much inclined to take it for granted that the bleaching action on a living animal goes on by the same process. This may be true of a bird's feather, which is considered histologically dead, yet it is hardly conceivable in a mammalian hair, which maintains throughout its life an active connection with the body; and, bearing this in mind, one may notice that the bleaching, which, if the tail were dead, one would expect to go on uniformly, starts at the tip, and gradually spreads downwards towards its base, thereby, to my mind, clearly showing that, although this lightening may, and probably does, take place by a merely mechanical process, yet such a process cannot act on the normal living hair. I may be perhaps allowed to mention on this matter, that when bleaching goes on among birds that bleaching process does not begin and continue slowly throughout the life of any particular feather, but a feather which may show hardly any change during the first six months of its life will suddenly undergo considerable disintegration and bleaching on the seventh. Does it not seem as though vital forces existed in that feather during the earlier part of its life? Taking our remarks on bleaching into a rather wider field, we find that this "fading" is restricted either to certain races, or to certain parts of the animals—for instance, among the large and closely allied Squirrels of the Ratufa bicolor group, as I have already shown in a previous paper, which inhabit the