2 FEATHERS CHAP. 
The aid of the Palaeontologist and Geologist must thus be called 
in to clear up many problems which present themselves to the 
Ornithologist who does not content himself with examining exist- 
ing forms of life alone. Archaeopteryx (p. 23) from the Jurassic 
System is the oldest Bird known, nor are any other pre-Tertiary 
forms recorded, save a small number from the rocks of the Creta- 
ceous Epoch, the chief of which are the so-called Odontornithes, 
or toothed species of America (p. 49). 
The following paragraphs on the structure of Birds will help 
to explain the systematic account in the later chapters. 
Feathers.—Returning to the outward character denoted by 
the popular saying with which we began, the Feathers’ con- 
stituting the plumage may not inconveniently be first considered. 
The general belief that they grow from almost every part of a 
Bird’s body, as do hairs in most Mammals, is erroneous; for, 
almost without exception, they grow in certain definite tracts 
called pterylae, the intervening spaces, whether they be wholly 
bare or covered with down, being termed apteria. The arrange- 
ment of these patches is at times of considerable assistance in 
determining a Bird’s affinities ; and the subject may be studied in 
Nitzsch’s Pterylographie* or in a shorter form in Dr. Gadow’s 
article “ Pterylosis” in Professor Newton’s Dictionary of Birds. 
A feather originates thus. A conical papilla arises in the 
derma and pushes up the epidermis, a depression forming mean- 
while around the base; subsequently the derma supphes a 
nutritive pulp, while part of the epidermal layer is converted 
into a tuft of stiff rays, meeting and forming a short tube 
below ; these thereafter burst their covering and protrude as the 
rami or barbs, on which, apparently by secondary splitting, are 
commonly produced radii or barbules. In this state we have a 
“plumule” or “down-feather” ; but in the case of the feathers that 
have “webs” or “vanes” (veailla) often called contour feathers 
(pennae or plumae), afresh papilla forms at a deeper level, so that 
the earlier structure is thrust forward and eventually drops off 
from the apex of the later. Meanwhile the “ dorsal” portions of 
1 The integument of a Bird consists of Skin and Feathers, the former being 
composed of a superficial epidermis and an underlying derma or cutis, which 
is rich in sensory organs but poor in blood-vessels. The epidermis itself has 
a horny outer layer and a softer (Malpighian) substratum. Feathers, hairs, bristles, 
scales, claws and bill-sheaths are epidermal structures. 
* A translation was edited for the Ray Society by Mr. Sclater in 1867. 
