MASCHA] STRUCTURE OF WING—FEATHERS II 
A comparison of these measurements shows how great, especially 
in Cygnus olor, is the increase in height of the secondary quills 
from the base to the middle of the feather. The decrease in height 
towards the end of the feather is gradual, the secondary quills 3 cm. 
from the tip of the feather are sometimes considerably higher than 
at a similar distance from the base. 
We know that the development of the parts corresponds to the 
demands made upon them and that in general an organ is most 
strongly constructed and most capable of resistance exactly at the 
point where this strength is most needed. The task of these feathers 
is to bear and to raise the bird’s body, by pressing on the air below, 
therefore the secondary quills are highest and as a consequence the 
feather vane the strongest and most capable of resistance where the 
greatest force is to be withstood. The wing being a concave surface, 
we can assume that its parts will be subjected to different pressures, 
and further, that where the pressure is greatest the feathers will be 
strongest. Apart from the variations of curvature we must also 
take into consideration the length of the feathers relative to the 
whole wing. In Diomedea the arm-remiges are short in comparison 
to the length of the wing and the secondary quills highest at the base. 
Where the remiges are relatively long, the secondary quills attain 
their maximum height in or just above the middle of the feather. 
The functional meaning of this correlation is however not quite 
easy to make out, but physiologists and flight-engineers should pay 
due attention to the fact that such morphological peculiarities are 
always correlated to the mechanical or other demands. 
In addition to these general remarks on secondary quills I must 
mention the peculiar structure of the margin of the outer vane of 
the three outermost remiges in owls, which are toothed or rather 
comb-shaped (figs. 31, 34 7). The finer structure of this comb how- 
ever seems not to have been understood; its teeth are nothing else 
than the tips of the secondary quills of the outer vane, which in this 
instance, do not bend inward terminally and lie close together, but, 
after extending in a straight line for some distance, suddenly bend 
outward, so that their ends stand almost at right angles to the direc- 
tion of the primary quill. Of course the separate teeth of this comb, 
as parts of the secondary quills, are provided with tertiary fibers 
(fig. 34). It is to be noted that this formation, which is absent in 
only few species of owls, as for instance in Nyctea nivea, a day bird 
of prey, is to be found also in some of the Caprimulgi (e. g., some 
species of Podargus, fig. 30, Z). On the other hand, they seem to be 
entirely absent in the genus Caprimulgus itself, nor do they occur in 
Stringops habroptilus, although it also is a night bird. 
