do those in possession exert themselves to expel the intruder, who is generally equally determined to remain. Far less brave is the Swallow when brought into collision with its principal enemy, the Sparrow; it often happens that no sooner is the Swallow's nest completed than a male Sparrow creeps in and takes possession, keeping guard at the door, in order to prevent the entrance of the rightful owner; under these circumstances, the latter, not venturing to obtain admittance by force, usually summons its companions, who together beset the impudent intruder with loud cries and every demonstration of anger. In most cases the Sparrow retains possession of its ill-gotten abode, but should the Swallow be bold, a battle sometimes takes place that proves fatal to one or other of the combatants. So constant are these attempts of the Sparrow to obtain a home for its young, that a pair of Swallows sometimes are deprived _twice_ in the season of the domicile they have laboriously completed, and, should this occur, do not breed at all that year. It was formerly imagined that the Swallow revenged itself on its foe by building it up in the nest, but we need hardly say that this is untrue. The Martins make their appearance in England a few days after the Chimney Swallow (_Cecropis-Hirundo-rustica_), and on their arrival are usually seen in warm and low situations, such being most likely to supply an abundance of their natural food. They are equally distributed throughout the kingdom, and are found wherever man has fixed his residence, seeming to court his protection. They commence nidification early in May, and build in the upper angles of windows and under the eaves of houses, sometimes under the arches of bridges or against the face of rocks. The nest is formed of mud completely worked and cemented, and is closed all round except a small orifice, usually on the sheltered side, just of sufficient size to permit the passage of the inhabitant; the interior is well lined with a collection of straw, hay, and feathers. These birds leave us in October; preparatory to their departure, they congregate in great numbers on the roofs of houses. * * * * * The MOUNTAIN or SHORE SWALLOWS (_Cotyle_) are recognisable by their slightly forked tail, and lax, lustreless plumage. Two species are indigenous to Europe; a description of these will serve for the entire group. THE ROCK SWALLOW.