ORDER PASSERES. 497 



parts numerous hairs could be observed 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 yellov/. 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 tint of white. The absurdity of this supposi- 

 tion is too apparent to be further exposed. 



*' With respect to the opinion which we have advanced, it 

 appears 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 during the course of a single 

 night ; but we think that the particular observations on the 

 ermine warrant us in believing, that the change of colour in 

 the alpine hare 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 necessary. In these changes 

 the range of colour is from blackish-gray, through gray to 

 white, an arrangement so nearly resembling that which pre- 

 vails 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 inde- 

 pendent of the ordinary annual moultings of the birds. 



