? 
362 M.V. Fatio on the Coloration of Feathers. 
4. Small lateral hooklets, forming, as it were, the branches of 
the latter, or quaternary axes. 
I may then indicate that each of these parts is also composed 
of an exterior epidermis with flat and irregular cells, of a cortical 
matter formed of cells more or less elongated into fibres, of a 
coloured medullary substance in rounded or polygonal cells in 
the interior, and of pigment-granules scattered or grouped in the 
centre of each segment of each axis. 
Lastly, I may state that the feather is formed in the interior 
of the corium at the expense of plastic cells which become 
organized in a protective sheath, and that, in growing, they 
push before them the down which prepared their path in the 
young bird. 
Cuvier*, Reclam+, Engelt, Holland§, and many others have 
written so much upon the development of feathers, that [ may 
abstain from touching upon this point. When once grown, the 
feather has already received all the coloured principles that it 
can ever derive from the body; the bloodvessels which have 
nourished it become gradually obliterated, and its interior me- 
dulla dries up by degrees. 
This being established, I commenced by studying the modifi- 
cations due to actual moultings, or to changes of feathers; but 
I shall not enter here into any details, in order to arrive more 
speedily at the true purpose and actual result of my investiga- 
tion—namely, the various modes of coloration in the same 
feather. 
Every bird presents different aspects according to its age and 
sex and the season ; but it also varies according to the localities 
which it inhabits, and the food which it finds there. The blood, 
modified by these various internal or external influences, fur- 
nishes the new feathers with diversely elaborated pigments. 
A young bird, for example, at its first moult, will not receive 
either the same quantity or the same quality of pigment as an 
older individual. A male will not receive the same colouring 
matter as his female, or, rather, he will receive a substance 
which, although at first analogous, will be capable, of modifica- 
tion in a different manner. Lastly, an old individual will always 
receive only the same quantity of the same pigment, so as con- 
stantly to present a similar plumage. 
* F. Cuvier, Observ. sur la Structure et le Développement des Plumes 
(Mém. du Musée d’Hist. Nat. tome miii.). 
+ C. Reclam, De Plumarum Pennarumque Evolutione. Leipzig, 1846. 
t Jos. Engel, Ueber Stellung und Entwickelung der Feder (Wiener 
Sitzungsber. Bd. xxi., 1857, pp. 376-393). 
§ F. Holland, Pterologische Untersuchungen (Journal fiir Ornitho- 
logie, 1864, vol. xi.). 
