Until within the last few years the changes of color in the fur of mammals (as in the ermine in winter), and in the plumage of birds in the season of reproduction, were supposed to be effected by the simple reproduction of the hairs and feathers; but this cannot be the case, as many facts go to prove that these changes occur at other times than the period of moulting, and without the loss of a hair or feather. It is well known that vivid emotions of fear or grief may turn the human hair gray or white in so short a period that there could be no change in the hair itself to account for it; and a case is on record of a starling which became white after being rescued from a cat. It has been maintained by Schlegel and Martin that many birds always get their wedding plumage without moulting. The fact being admitted, how can the change of color be explained in the mature feather, which has no vascular or nervous communication with the skin ? The wearing away of the light tips, mentioned by Mr. Yarrell, is not only unphysi-ological, but in most cases does not happen.

Dr. Weinland, from the examination of bleached specimens in museums, and of recent birds, expresses the belief that the brightness and fading of the colors are owing to the increase or diminution of an oily matter in the feathers; the microscopic examination of the web of feathers from the breast of a fresh merganser {mergus serrator, Linn.) showed numerous lacuna of a reddish oil-like fluid; some weeks after, the same feathers, having become nearly white from exposure to light, disclosed air bubbles instead of the reddish fluid; from this he concludes that the evaporation of the oily fluid, and the filling of the spaces with air as in the case of the white water lily, produces the changes of color. If this fluid be oily, as there is good reason to believe, mere physical imbibition would be sufficient to introduce it into the dead feathers, as it is well known that fat passes through all tissues very readily, even through compact horn. In the season of reproduction, the nutritive and organic functions are performed with their utmost vigor, and the supply of fatty coloring matter would flow freely to the feathers; under the opposite conditions of debility, cold, or insufficient food, the oily matter would be withdrawn and the feathers would fade.-In regard to the value of feathers to man, it will be sufficient to enumerate the ornamental employment of the plumes of the ostrich, egrets, cranes, and peacock; the economical uses of the down of the eider duck and the plumage of the goose; the importance of the goose quill before the introduction of steel and gold pens, and the adherence of many at the present day to the more perishable, less convenient, but softer-moving quill; not to more than allude to the consumption of the plumage of the gorgeous tropical birds in the manufacture of feather flowers, and the utility of the downy arctic skins as articles of dress in the regions of perpetual snow.