ment, and presents every possible variety of tint and texture. Well have they been described by the poet:

"In plumage delicate and beautiful,

Thick without burthen, close as fishes' scales,

Or loose as full-blown poppies to the breeze;
With wings that might have had a soul within them,
They bore their owners by such sweet enchantment."

MONTGOMERY'S "PELICAN ISLAND."

An illustration of the buoyancy of birds, and the power of their descent, is furnished by the Gannet or Solan

Goose (Fig. 168) of our own shores. When searching for food it flies a short way above the surface of the water; on

seeing a fish, it rises into the air, and descends with such rapidity and force as to secure the prey. Some idea of the power of its descent may be formed from a circumstance related by Pennant. One of these birds, flying over Penzance, saw some Pilchards spread out upon a fir plank about an inch and a half thick, and which was used in the curing of the fish, and darted down with such violence that it struck its bill quite through the board, and broke its neck. Pennant adds, that these birds are sometimes taken at sea by a similar deception, a fish being fastened for the purpose to a floating plank.

The stomach of birds differs greatly according to the nature of their food. In those which live on flesh it is thin and membranous, but in others the sides are of great thickness, and being moved by powerful muscles, act as a mill in grinding down the food. The stomach in this thickened

state is well known as the gizzard, and its action is aided by small pebbles, and other hard substances, swallowed by the bird. This instinctive action is one well known in our common barn-door fowl; and in the Ostrich (Fig. 169) it prevails to such an extent, that in the stomach of one were found pebbles enough to fill a large glass bottle. As this bird will swallow metals with equal readiness, popular credulity, in former times, went so far as to assign to it the power of digesting these substances; and many are the allusions in the older writers to this supposed power of "the iron-eating Ostrich."

Birds possess in a high degree the sense of sight; and the eye is so admirably adapted to their wants, that it is suited for vision at the great height to which birds soar, and no less fitted for vision near at hand. It has three, not two eyelids; the third one, when not in use, lies in the inner angle of the eye.

The sense of smell is also very highly developed, and various experiments have been tried to ascertain the extent to which it exists in different species. It has been a matter of controversy whether Vultures are guided to the carrion on which they feed by the sense of sight or that of smell; but there seems no good reason for doubting that both senses are made to contribute to the welfare of the birds by directing them to their prey. The far-sighted eye sees it from the clouds, and the characteristic flight of the Vulture, as it descends to the feast, reveals to its brethren the fact that a repast is spread for them; and from all quarters they hasten to participate. And, again, when near at hand, under the screen of cliffs, or the thick-tangled vegetation of tropical forests, the sense of smell reveals the hidden carcass, and tempts

around it those who act an impor- Fig. 170.-POUCHED ADJUTANT. tant part as agents for its removal.

There are many other birds which, like the Vultures, assist in freeing the surface of the earth from decaying animal matter. Thus, in India, there is one whose services are no less valuable, a gigantic kind of Crane, called the Adjutant (Fig. 170). This bird is of such utility as a scavenger, that it is not only permitted to remain unmolested, but it is held in great estimation, and even regarded with reverence. It is a voracious feeder, and gulps down its food whole. It has been known to swallow a leg of mutton of five or six pounds weight; and Sir Everard Home states, that in the stomach of one, a Land Tortoise ten inches long, and a large black Cat, were found entire.

Migration.-At the approach of winter, there are various birds which make their appearance pretty nearly at the same time each year, and leave us early in the spring. They have arrived from regions further north, and have made our islands the southern limit of that periodical change of residence to which we give the term migration. There are others whose appearance in spring we welcome, not only because of the beauty of their flight or their plumage, or the cheerfulness of their notes, but as the heralds of brighter skies, and returning verdure. These stay with us during the summer, and then wing their way to the south. The British islands constitute the northern limit of their migration. It is now ascertained, that the greater number of these summer birds leave these kingdoms for the north and west of Africa, whence they return every year, with such punc