A History 
- of jBirds. 
(109) THE BIRD WORLD. 
A History of Birds. 
By W. R PYCRAFT, A.L.S., F.Z.S., Etc. 
(Continued from p. 73). 
CHAPTER II. 
CONCERNING FEATHERS. 
Though feathers are so common, so easily pro¬ 
cured, yet but few people, even Ornithologists, 
realise what marvels of structural beauty, what 
wonders of mechanism, they are; nor is the 
peculiar fashion of their distribution over the 
body now generally recognised. Those who have 
spent their lives in the study of lme birds, as 
many of my readers have doubtless done, need 
not be told that the feathers of a bird are peculiar 
in that they are not, as a rule, generally or evenly 
distributed over the body after the "fashion of 
hairs on a dog, for instance, but, on the con¬ 
trary, are arranged in long and generally narrow 
bands or “ tracts,” separated by wide, bare, or 
sometimes down-clad, spaces. The fact that 
these bands vary greatly in shape among birds 
was first realised by a German naturalist named 
Nitzsch, who made a long and careful study of 
the feather tracts of all the birds he could "get 
hold of. As a result of his patient work he was 
able to show that the variations in this arrange¬ 
ment followed certain definite lines, each group 
of birds possessing a type peculiar to itself, and, 
for the purposes of convenient description, he 
gave these tracts distinctive names, which, in the 
main, are followed to this day. 
Distribution of Feather-Tracts. 
Briefly, as a result of his work, he distin¬ 
guished : (1) a head tract, formed by the feathers 
clothing the head; (2) a spinal tract, extending 
from the head down the back of the neck, and 
along the back to the tail; (3) a ventral tract 
running from the throat down to the base of 
the neck, where it branches at the shoulders, to 
run down over the breast and abdomen in the 
form of two bands, a broad outer, and a narrow 
inner band; (4) a pair of humeral tracts, which, 
crossing the upper arm, form the feathers known 
as the scapulars; (5) the wing tract, including the 
quills and wing-coverts; (6) the tail tract; (7) the 
femoral tracts, which run across the thighs; (8) 
the leg tracts, which cover the legs below the 
knee. 
Differences in Various Groups. 
The most important of the variations which 
these tracts present are to be found in the spinal 
and head tracts. Thus, in the first named, the 
spinal tract, in the Swifts, encloses a bare 
space over the middle of the back; while in the 
Swallows it divides into a fork in this region, 
leaving the hinder portion of the tract in the 
form of the usual straight band. In the Finch 
tribe the middle region of this tract is diamond- 
shaped. The head tract, again, often encloses a 
space; as, for example, in the Humming-birds 
and Mouse-birds of Africa. The ventral tract 
similarly presents very marked differences when 
a number of different kinds of birds come to be 
examined. 
A Simple Investigation. 
Those who may be interested in this question 
should take, say, a Sparrow, Starling, Thrush, 
Pigeon and Fowl, cut off the feathers with a pair 
of scissors close to the body, and compare the 
difference. Since these differences are constant, 
and since each group presents a type of its own, 
it has been found that the “ pterylosis,” as this 
arrangement of the feathers is called, affords a 
valuable aid to the classification of birds. For 
example, the very wide difference in the pterylosis 
of the Swifts and Swallows was the first indica¬ 
tion of the fact that these birds were not related, 
as they had always been supposed to be, and later 
anatomical investigation has given further proof 
that these birds belong to quite different groups. 
In the Penguins and the Ostriches the bare 
spaces so conspicuous in other birds are hardly 
traceable, the feathers covering almost every inch 
of the body. 
The Various Types of Feathers. 
So far we have spoken only of the feathers 
which form the outer surface covering of the 
bird, the “ Contour ” feathers, as they are called, 
because they form the contour or outline of the 
body. But besides these there are no less than 
three other distinct kinds of feathers—down- 
feathers, filo-plumes, and powder-down. 
Down-feathers in many birds are conspicuous 
by their absence, and are developed most abund¬ 
antly in water-birds, such as Ducks for example; 
growing not only between the feathers, but over 
the otherwise bare spaces as well, so as to form 
a thick undergrowth answering to the under-fur 
of seals, for instance. 
Filo-plumes appear to be present in all birds. 
They are the long, hair-like growths so con¬ 
spicuous in the common Fowl when plucked. In 
some birds they attain such a length as to 
extend beyond the contour feathers, forming, as 
in some Cormorants, long white delicate plumes. 
The Powder-down feather': are found only in a 
few groups, such as the Herons and Bitterns, 
and some Hawks and Parrots. In the Herons 
and Bitterns they form large patches, a pair on 
the breast, and a patch over each thigh. Of a 
peculiar woolly appearance, they are remarkable 
