302 LEPORID^— LEPUS 



supported a change in pigmentation without actual renovation 

 of the fur either in spring or autumn. All modern observers 

 are in agreement that the vernal replacement of white by brown 

 is due to a moult and casting of the white hairs ; the autumnal 

 blanching, on the other hand, is still variously attributed to 

 moult or to actual abstraction of pigment from the hairs. The 

 latter view was taken by Welch (Proc. Zool. Soc, London, 

 1869, 228-236), and in 1874 by Alston when editing Bell's 

 second edition. It was utilised by Poulton as the chief basis of 

 his theory on variable protective resemblances in vertebrates 

 (see The Colours of Animals, 1890, chap, vii.), and was 

 generally accepted until, in 1894, Allen (Btill. Amer. Mus. Nat. 

 Hist., vi., art. iv., May 1894, 107-128) asserted that in Lepus 

 americanus both autumnal and vernal changes are accomplished 

 by moult, a view supported by Collett in regard to L. timidus 

 in Norway. Allen was not aware if the underfur of American 

 hares is shed in autumn, but Nelson states (op. cit. supra, ^8) 

 that in these the underfur does not whiten as it does in 

 European forms. 



The first British writer to arrive at the truth seems to have 

 been MacGillivray, whose discovery that the pelage is almost 

 always undergoing alteration and renewal cannot be con- 

 troverted ; while his apparently contradictory belief that 

 nevertheless "sometimes the brown hairs themselves, on the 

 application of intense cold, become whitened " (see William 

 MacGillivray's Life of William MacGillivray, 19 10, 130) has 

 been corroborated by Metchnikoff. The latter, who has since 

 been supported by Tomasczewski and Erdmann {Miinchener 

 medic. Wochenschr., 1906, 359), showed [Ann. de £ Institut 

 Pasteur, 1901, 865, pis. 13, 14, and Proc. Roy. Soc, London, 

 lxix., 1902, 156) that, in senescence of old men and dogs, 

 large cells, which he named chromophages ("colour-eaters"), 

 issuing from the central medullary parts of the hairs, enter 

 the cortical layers, where they engulph and remove the 

 granules of pigment. The process may thus be classed 

 under the general laws of atrophy of solid portions of an 

 organism. In a later paper {Compt. rend. Acad. Sci., cxlii., 

 No. 19, 7th May 1906, 1024-1028) Metchnikoff reported that 

 the same facts apply to the hairs of Lepus timidtis and the 



