388 



HYBERNATION. 



Animals 

 which 



unlike that of the inferior animals, is always dark at the 

 base, and still continues so during the change to grey ; 

 am- of 6 ' 1ence we are disposed to conclude from analogy, that 

 thejr the change of colour, in those animals which become 

 Clothing, white in winter, is effected, not by n renewal of the hair, 

 > -Y"""*' but by a change in the colour of the secretions of the 

 rcte mucosum, by which the hair is nourished, or per- 

 haps by that secretion of the colouring matter being di- 

 minished, or totally suspended. 



As analogy is a dangerous instrument of investiga- 

 tion in those departments of knowledge which ultimate- 

 ly rest on experiment or observation, so we are not dis- 

 posed to lay much stress on the preceding argument 

 which it has furnished. The appearances inhibited by 

 a specimen of the ermine now before us are more satis- 

 factory and convincing. It was shot on the 9th May 

 (1814-), in a garb intermediate between its winter and 

 summer dress. In the belly, and all the under parts, 

 the white colour had nearly disappeared, in exchange 

 for the primrose yellow, the ordinary tinge of these 

 parts in summer. The upper parts had not fully ac- 

 quired their ordinary summer colour, which is a deep 

 yellowish brown. There were still several white spots, 

 and not a few with a tinge of yellow. Upon examining 

 those white and yellow spots, not a trace of interspersed 

 new short brown hair could be discerned. This would 

 certainly not have been the case if the change of colour 

 is effected by a change of fur. Besides, while some 

 parts of the fur on the back had acquired their proper 

 colour, even in those parts numerous hairs could be ob- 

 served of a wax yellow, and in all the intermediate 

 stages from yellowish brown, through yellow, to white. 



These observations leave little room to doubt, that 

 the change of colour takes place in the old hair, and 

 that the change from white to brown passes through 

 yellow. If this conclusion is not admitted, then we 

 must suppose that this animal casts its hair at least 

 seven times in the year. In spring, it must produce 

 primrose yellow hair ; then hair of a wax yellow ; and, 

 lastly, of a yellowish brown. The same process must 

 be gone through in autumn, only reversed, and with 

 the addition of a suit of white. The absurdity of this 

 supposition is too apparent to be farther exposed. 



With respect to the opinion which we have advanced, 

 it seems to be attended with few difficulties. We urge 

 not in support of it, the accounts which have been 

 published of the human hair changing its colour in the 

 course of a single night; but we think the particular 

 observations on the ermine warrant us in believing that 

 the change of colour in the alpine hair is effected by a 

 similar process. But how is the change accomplished 

 in birds ? 



The young ptarmigans are mottled in their first 

 plumage similar to their parents. They become white 

 in winter, and again mottled in spring. These young 

 birds, provided the change of colour is effected by 

 moulting, must produce three different coverings of 

 feathers in the course of ten months. This is a waste 

 of vital energy, which we do not suppose any bird in 

 its wild state capable of sustaining; as moulting is the 

 most debilitating process which they undergo. In 

 other birds of full age, two moultings must be neces- 

 sary. In these changes, the range of colour is from 

 blackish grey through grey to white, an arrangement 

 so nearly resembling that which prevails in the ermine, 

 that we are disposed to consider the change of colour 

 to take place in the old feathers, and not by the growth 

 of new plumage ; this change of colour being indepen- 

 dent of the ordinary annual moultings of the birds. 



colour of 



their 

 Clothing. 



Independent of the support from analogy which the AnimaU 

 ermine furnishes, we may observe that the colours of which 

 other parts oi' a bird vary according to the season. ch:i "g c 

 This is frequently observable in the feet, legs, and bill. 

 Now, since a change takes place in the colouring secre- 

 tions ol'theso organs, what prevents us from supposing 

 that similar changes take place in the feathers ? But 

 even in the case of birds, we have before us an ex- 

 ample as convincing as the ermine already mentioned. 

 It is a specimen of the little auk, (Alca al/?,) which was 

 shot in Zetland in the end of February 1810. The 

 chin is still in its winter dress of white, but the feathers 

 on the lower part of the throat have assumed a dusky 

 hue. Both the shafts and webs have become of a 

 blackish grey colour at the base and in the centre, 

 while the extremities of both still continue white. The 

 change from black to white is here effected by passing 

 through grey. If we suppose that in this bird Hit 

 changes of the colour of the plumage are accomplished 

 by moulting, or a change of feathers, we must admit " 

 the existence of three such moulting s in the course 

 of the year one by which the white winter dress is 

 produced, another for the dusky spring dress, anil a 

 third for the black garb of summer. It is surely un- 

 necessary to point out any other examples in support 

 of our opinion on this subject. We h;tvc followed 

 nature, and our conclusions appear to be justified by 

 the appearances which we have describe:!. 



Having endeavoured to ascertain the manner in which Causes oi 

 this change of colour takes place, we are now ready to the change 

 investigate the causes by which it is produced. As this 

 change of colour in winter is peculiarto the animals which 

 inhabit cold countries, we may safely conclude, that tem- 

 perature exercises over it a powerful influence. This 

 supposition is countenanced by the slowness of the pro- 

 cess of change of colour in a mild autumn, and its im- 

 perfect accomplishment during a mild winter. Besides, 

 in some animals, such as the black guillemot, the change 

 is never complete in the more temperate regions, but 

 becomes more perfect as we proceed northwards, until 

 at Greenland the bird is of a pure white. If this change 

 of colour proceeds from a renewal of feathers, here at 

 least the colour of the feathers must be considered in- 

 fluenced by the temperature, and consequently a cor- 

 responding influence must be exercised on the secreting 

 organs. 



The distribution of colour in the animal kingdom in 

 general seems to follow the same law ; the deep and 

 bright colours prevailing in the warm regions, while 

 the tints of the colder regions are pale and dull. Are 

 we to conclude, that cold diminishes the action of the 

 vessels which furnish the colouring matter, and, when 

 intense, entirely suspends their functions ? or are we 

 to consider light as in part concerned in producing 

 the effect ? In general, the fur of quadrupeds, and 

 the feathers of birds, are darkest where exposed to 

 the light, and are pale coloured towards the hase ; but 

 in the instances before us, this difference disappears, 

 and a complete uniformity in all the parts of the cover- 

 ing prevails. Besides, the change does not take place 

 on all parts of the body at the same time, but appears 

 in spots, or on single hairs or feathers. Light tlierefore 

 has little influence. 



There is another agent besides cold apparently con- 

 cerned in the change in. the colour of the feathers of 

 birds. In all birds the feathers become more vivid in 

 spring, and certain spots appear which are not obser- 

 vable at other seasons. This brightness of plumage 

 and these spot* continue only during the season of love; 



