A History 
of Birds. 
( I 53) 
THE BIRD WORLD. 
A History of Birds. 
By W. P. PYCRAFT, A.L.S., F.Z.S., Etc. 
( Co?itinued from f. 124). 
Now, when the wing is extended, each of these 
sequents is found, on examination, to support a 
series, or row, of conspicuously long feathers— 
at least, in a long-winged bird. These are the 
primaries and secondaries, or “ flight feathers,” 
and the feathers of the upper arm, which are 
known as the “ tertiaries,” or technically as the 
“parapteron” and “ hypopteron,” for, unlike the 
two first-named series, the flight-feathers, they 
form a double series, one above the other. Their 
use is to fill up the gap that would otherwise 
be left between the innermost flight-feathers and 
the body, which gap, unfilled, would seriously 
hamper flight. These feathers can best be seen 
in a wing from which all other feathers have 
been removed, as in Fig. 2. The “other” 
feathers, just referred to, are known as the 
coverts, and they form several well-defined rows, 
known as the major coverts, medium coverts, 
minor coverts, and marginal coverts (Fig. 3), 
and they present, among different birds, very 
different characters, in so far as the number of 
rows and their “ overlap ” is concerned. As to 
the number of rows : these vary only in so far 
as the minor and marginal coverts are con¬ 
cerned. Neither on the upper nor the under 
surface do the major or medium coverts exceed 
one row, but the minor coverts may number as 
many as six or more, or they may be altogether 
absent. The marginal coverts, which are the 
smallest in the wing, and clothe its front or 
anterior margin, though varying in number, are 
always represented by several rows. The matter 
of their overlap is important, and must be care¬ 
fully studied both by artists and those who are 
engaged in the difficult problem of the classifica¬ 
tion of birds. The major coverts, which imme¬ 
diately overlie the flight-feathers, always overlap 
one another in such a way that their free edges 
are turned towards the tip of the wing. The 
other coverts vary, in this respect, in different 
grcups of birds, so that in some the free edge 
is turned towards the tip of the wing. The 
few of the innermost have their free edges 
directed outwards. 
On the under surface of the wing the medium 
coverts are in many birds wanting or incom¬ 
pletely developed. The minor coverts are often 
entirely wanting, while the marginals—those, at 
least, nearest the hinder border of the wing— 
are commonly of considerable length, and cover 
up what would otherwise be a bare space along 
the under side of the wing. 
The Action of the Wings. 
But. this question of overlap plays a much 
more important part than any yet mentioned—at 
any rate, in so far as the flight-feathers are con¬ 
cerned. These, it is to be notiped, like the 
major, or “ greater,” series of coverts, are so- 
arranged that their free edges, when the wing 
is extended, are turned towards its free edge. 
The full meaning of this will become clear 
directly the part these quills play is remembered,, 
for as the wing is raised the air forces 
its way between the feathers. At the downward 
beat, however, the webs, or vanes, of the feathers 
are pressed closely one against another, so as to- 
form a continuous, unyielding surface, whereby 
the body is raised and propelled forwards. They 
have, then, these' quills, a valve-like action. 
Were the overlap of the opposite kind—“ proxi¬ 
mal ” instead of “ distal ”—the unyielding surface 
would be formed on the up-stroke of the wing, 
while in the down-stroke all lifting power would 
be lost. Compared with the bat’s wing, the 
wing of the bird is vastly superior, and for 
this reason : The wing of the bat is formed by a 
membrane stretched between long and slender 
fingers, so that any serious injury to the wing 
membrane permanently disables the creature. 
The bird’s wing, on the other hand, has its flying 
membrane formed by a number of overlapping, 
elastic, ribbon-like structures—the quills—which 
are periodically renewed, and can be replaced if 
injured. 
The Problems of Flight. 
The analysis of the movements during flight 
bristles with difficulties, and is, moreover, so 
dependent upon dry and abstruse technicalities 
for explanation that it must suffice to give a 
brief summary of the main facts. These I have 
taken from a recent work by one of our greatest 
authorities on the flight of birds, Mr. F. W. 
Headley. His account of this intricate problem, 
though wonderfully clear, is too long and rather 
too technical for reproduction here, but, put 
briefly, he has shown that the bird propels him¬ 
self by virtue of the resistance offered by the 
wind to the down-stroke of the wing and the 
velocity of the flight. This velocity, by increasing 
the resistance, gives the wing, especially at its 
tip at the end of the down stroke, a grip of the 
air, so to speak, so that the bird literally shoves 
himself forwards, and slightly upwards, at each 
stroke, the wing-tip serving as a fulcrum, 
thereby raises and supports the body, and at the 
same time drives it forwards. At the end of the 
stroke the hand is bent upon the forearm at the 
wrist, while the- whole wing is raised over the 
back and swung forwards and downwards once 
more, the hand being straightened on the fore¬ 
arm at the top of the up-stroke. Thus the longer 
the wing the swifter the speed, a rule which is 
