The MARTIN or ROOF SWALLOW (_Chelidon urbica_) we have selected as the type of a group, recognisable by their slightly forked tail and strong feet, the toes of which are connected from the first joint, and, like the tarsi, are thickly covered with feathers. This bird is five inches and a half long, and ten and three-quarters broad; the wing measures four inches, and the tail two and a half. Upon the back the plumage is almost entirely of an uniform blueish black; the under side and rump are white. The eye is dark brown, the beak black, and the bare parts of the foot black. Both sexes are alike in colour, but the plumage of the young is less clear in its tints than that of the adult. The Martin inhabits the whole of Europe, and penetrates further north than the Chimney Swallow; it is numerous in Siberia, and during its migrations visits the interior of Africa and Southern Asia. In most respects it closely resembles the species already described, but is somewhat less brisk and intelligent; its flight also is not so rapid and varied as that of the Chimney Swallow, but it frequently soars to an enormous height in pursuit of the insects upon which it subsists. Its voice is very far inferior to that of the rest of its family, and its cry monotonous and harsh. In populous districts the nests of this bird are invariably constructed upon houses, but where human habitations are scarce, the Roof Swallow is content to make its preparations upon rocks, or any situation that will afford it a secure shelter from the wind and rain. The nest is very similar to that of the Chimney Swallow, but with this difference, that it is always built against a hole, and has no external entrance; sometimes many pairs construct their dwellings under the same eaves or the same rock, and thus form a kind of settlement. Although usually peaceful, during the breeding season disputes and battles are of constant occurrence; each couple naturally endeavouring to obtain the snuggest corner, and to oust its neighbour should the opportunity offer. The brood consists of from four to six delicate snow-white eggs, and the nestlings are hatched in about twelve days. The female alone broods, and is fed by her mate only when the weather is fine; the young also frequently have but an insufficient supply of food, owing to the difficulty of procuring insects when the season is inclement, and thus must very often be left behind when the flocks migrate, as they are still too weak to undergo such great fatigue. If all goes well, the nestlings are fully fledged in about sixteen days, but generally remain for some time longer under the care of their parents. During this period the whole family return at night to their nest, which they fill so completely that we have often been inclined to wonder that the walls did not give way under the pressure to which they were subjected. Desperate fights often ensue when a stray bird finds its way into a wrong nest, and most courageously