The effects of confinement in obstructing regular natural changes are manifested in a variety of instances : thus, the common squirrel, which, in the wild state, renews its fur in spring, obtaining a much coarser and redder coat, and, at the same time, losing the ornamental long hairs which, in winter, adorn its ears, rarely exhibits even an indication of this change when in captivity ; and it is well known that the linnet tribe, when under the restraint of the cage, display not the slightest trace of those seasonal brightenings, which so re- markably distinguish these birds in a state of freedom.

In- deed, in the latter instance, as the linnets breed prolifically in confinement, we can hardly assume that physical weakness is the cause of this; and it becomes difficult to assign to what external influence their summer brilliancy may be attributable, or, rather, to determine the reason of its suppression in, vigorous captive specimens.

The bleaching of cuticular productions by severe cold can hardly be esteemed analogous to other alterations of colour ; neither does it seem to be more akin to those sudden changes of the human hair to grey, which have happened during continued intense emotions of fear or anxiety.

It is, how- ever, difficult to assign to what extent the changes of arctic animals are dependent on external influence ; for though, in the ermine, they undoubtedly seem to be produced by tem- perature only, I think there is much reason to suspect that the double-moulting ptarmigan would become white in winter, even though removed from its frigid habitat.

This can only be ascertained by keeping them for some time in confinement, which I am not aware has ever been attempted.