COLOUR IN BIRDS AND QUADRUPEDS. 235 



is not, properly speaking, caniculated, the colouring matter being de- 

 posited by the papilla at the same time as the epidermic sheath.* The 

 chemical composition of feathers is believed to be nearly the same as 

 that of hair, nails, &c. consisting principally of inspissated albumen, 

 united with small portions of gelatine and animal oil; and it is a sub- 

 ject of inquiry what chemical action takes place, which imparts co- 

 lours not only to the shafts of the quill, but to the barbs, and even the 

 minute barbules attached to these barbs. Are these changes in colour 

 efifected by the action of the external atmosphere, or by a vital opera- 

 tion? As the air contained in the feathers is exposed to the influence 

 of the vascular pulp, may it not in this way produce a chemical action 

 on the colour of the feathers? Some birds certainly moult twice a 

 year, with the exception of their wing and tail feathers, which, in most 

 species, are only cast amiually. As the latter are longer in coming to 

 maturity, may not colours be imparted to them more slowly, and may 

 not this account for the changes of colour which are progressively 

 taking place in the bars on the tails of Hawks and other species ? 



These inquiries may be also attended with beneficial results to the 

 science of ornithology, in enabling us to discriminate the true from 

 merely nominal species. By a little attention to this subject, Wilson 

 was enabled to expunge from our nomenclature of birds many species 

 which Catesby, Edwards, Pennant, Latham and others had multiplied 

 to a great extent, and to extricate the science from difficulties which 

 were continually leading the student of nature into infinite doubts and 

 perplexities. Through this mean also, Bonaparte, Nuttall and Audu- 

 bon corrected some of the errors into which their predecessors, from a 

 want of opportunity for a fuller investigation of the subject, had fallen. 

 The work is not yet completed. By a further inquiry into the changes 

 in plumage to which birds are subject, species that are now supposed 

 distinct, may be found to be identical. Many new species of Gulls, 

 that have been multiplying in Europe and America, may prove to be 

 the young, or the winter plumage of species that have long since had 

 a name.f The long disputed, often rejected, and as often readmitted 



* Cruveilhier, Anatomie Descriptif, Tom. III., p. 420. 



t This genus requires a more careful revision. It will be found, on an attentive examina- 

 tion of the changes of plumage to which the species are subject, and on a comparison with 



VI. — 3 I 



