CLASS II. AVES 
5 
and frequently only acquire their mature dress after the lapse of three or four years, the plumage 
undergoing a certain change at each moult. These circumstances undoubtedly throw great diffi- 
culties in the way of the student of ornithology, and it is perhaps not much to be wondered at, if 
we have sometimes half a dozen different names for different states of the same species ; but it 
must also be confessed, that in this, as in other departments of natural history, the desire to de- 
scribe new species has often led to an unjustifiable multiplication of errors of this description. 
In a zoological point of view the greatest importance attaches to the feathers of the wings and 
tail, to which different names have been given. The quills are inserted into all the bones of the 
wing, but the longest are those attached to the bones of the hand, and to these the name of pri- 
maries is given. The feathers supported by the fore-arm are denominated secondaries, and those 
attached to the humerus tertiaries. The thumb 
also bears a few quills, which form what is called 
the alula, or bastard wing. These, and some 
other feathers to which pai'ticular names have 
been given, are shown in the annexed engrav- 
ing. The base of the quills is covered by a se- 
ries of large feathers called the wing coverts, 
which are also distiuguished into primary and 
secondan-y. The feathers of the tail are fur- 
nished with numerous muscles, by which they 
can be spread out and folded up like a fan. 
Their bases are also covered both above and 
beneath by smaller feathers, which arc called 
the tail coverts. 
It is impossible to conceive any covering more 
beautifully adapted to the peculiar wants of 
these creatures than that with which they are 
endowed by nature. All the feathers being di- 
rected backward, the most rapid motion through 
the air only tends to press them more closely 
to the body, and the warm air, confined among 
the inner downy fibers, is thus effectually pre- 
vented from escaping. In the aquatic birds the 
feathers are constantly lubricated by an oily se- 
cretion, which completely excludes the Avater. 
In the wings the quill-feathers exhibit in the 
highest degree a union of the two qualities of 
lightness and strength, while by their arrange- 
ment they can be folded together into a very small compass. 
In their reproduction birds are strictly oviparous. The eggs are always inclosed in a hard 
shell, consisting of calcareous matter, and, unlike the animals of some of the succeeding classes, 
birds, instead of abandoning the hatching of their eggs and the development of their offspring to 
chance, almost invariably devote their wJiole attention, during the breeding season, to this im- 
portant object, sitting constantly upon the eggs to communicate to them the degree of warmth 
necessary for the evolution of the embryo, and attending to the wants of their newly-hatched 
young, until the latter are in a condition to shift for themselves. 
Most birds live in pairs during the breeding season, which usually occurs only once in the year; 
in many cases the conjugal union is for life. Both sexes generally take an equal part in the care 
of the young. They usually form a nest of some description for the reception of the eggs ; this 
is composed of the most diverse materials, such as sticks, moss, wool, vegetable fibers, &c.; in 
many instances the work of these little architects must excite the admiration of every observer. 
The nests of different individuals of the same species are generally not only of the same form, but 
even composed nearly of the same materials, so that a person, accustomed to the inspection of 
A, ear coverts; B, bastard wing; ODE, -wing coverts; ¥, prima- 
ries; G, scapulars; H, secondaries; L, tail coverts; K, under 
tail coverts, not shown. 
