AVES. 
162 
which we can have no idea, and from the most ancient times has caused to he attri- 
buted to them, by superstitious persons, a power of announcing future events. It is , 
doubtless upon this faculty that the instinct depends which [periodically] agitates 
migratory Birds, and impels them to direct their course towards the equator when 
winter approaches, and pole-ward at the return of spring.* They are not devoid of 
memory, and even imagination — for they dream ; and every body knows with what f 
facility they may be tamed, taught [in numerous instances] to perform various services, 
and to retain airs and words. 
DIVISION OF THE CLASS OF BIRDS INTO ORDERS. 
Of all classes of animals, that of Birds is the most strongly characterized, that in 
which the species bear the greatest mutual resemblance, and which is separated from g 
ail others by the widest interval. 
Their systematic arrangement is based, as in the Mammalia, on the organs of man- 
ducation or the beak, and on those of prehension, which are again the beak, and more 
particularly the feet. [The configuration of the sternal apparatus, also, (which we 
have illustrated by numerous figures,) and the modifications of the digestive and some- 
times vocal organs, supply highly important characters on which to ground the 
subdivisions.] 
One is first struck by the character of wehhed feet, or those wherein the toes are | 
connected by membranes, that distinguish all swimming Birds. f The backward position' 
of their feet, the elongation of the sternum, the neck, often longer than the legs, tojJ 
enable them to reach below them, the close, shining plumage, impervious to water,-S^ 
altogether concur with the feet to make good navigators of the Palmipedes. S' 
In other Birds, which have also most frequently some small web to their feet, a^i 
least between the two external toes, we observe elevated tarsi ; legs denuded of featherS! 
above the heel-joint; a slender shape; in fine, all the requisites for fording alongj 
shallow water, in search of nourishment. Such, in fact, is the regimen of the greate^ 
number ; and, although some of them resort exclusively to dry places, they are never'^| 
theless termed Shore-birds or Waders. ! 
Amongst the true land-birds, the Gallinacew have — like our domestic Cock — a heavy!- 
carriage, a short flight, the beak moderate, its upper mandible vaulted, the nostrils 
partly covered by a soft and tumid scale, and almost always the edges of the toes v 
indented, with short membranes between the bases of those in front. They subsist „ 
chiefly on grain. 
Birds of prey have a crooked beak, with its point sharp and curving downward ; | 
and the nostrils pierced in a membrane that invests its base : their feet [save in the-; 
Vulture group] are armed with stout talons. They live on flesh, and [the Vultures ; 
more the extraordinary fact (familiar to all practical observers) of 
Birds of passage, unless when driven by stress of weather, returning, :', 
both in summer and winter, to their former place of abode, and this u 
even when reared in confinement, and released immediately previous : 
to their first journey. — Ed. (See note to p. 31.) Vf 
t It is most difficult thus to generalize in the class of Birds. Eord ^ 
instance, the Gallinules, or Moorhens^ — habitual swimmers, — have no ; ' 
connecting membrane to the toes ; while the Terns, which are never 'j j; 
seen to swim, have their toes completely webbed, &c. Even the Herons; 'I |i ( 
„ . , „ . . . „ . , llie Curlews, and numerous other waders, will sometimes take the ' ' | 
animals to travel in the right direction; and the marvel increases water of their own accord, and swim across pools, though their struc- ij 
wlien we consider the length of route ordinarily traversed, and still ! ture does not indicate such a habit. — Ed. ! 
♦ It IS certain, however, that the rapid enlargement of the sexual 
organs is the immediate stimulant to migration in the spring ; while 
decline of temperature, most generally, is the directly predisposing 
agent in the autumn : this is manifest in the case of migratory Birds 
kept in confinement. The instances of the Swift, and adult Cuckoo, 
retiring southward at the hottest season of the year, are more difficult 
of explanation, and indicate some ulterior agency not hitherto divined ; 
though they do not affect the multitudinous observations, which con- 
clusively prove the influence of decline of temperature. It is less easy 
to imaeine nhvsical acenev that should constantlv imnel miirratorv 
