to shut up in an enclosure, with a wire screen overhead, a pair of birds brought up in isolation from their kind, with a view to find out what manner of nest their inexperienced efforts would produce. But, even though we have not such evidence, there are plenty of other proofs which confirm Mr. Wallace's theory.
The form and structure of birds'-nests are more dependent than is usually supposed upon external conditions, and consequently they vary in proportion as these conditions are changed. Each separate species employs the materials it has at hand, chooses sites most agreeable to its habits; and the shape given to the nests often betrays very definite purposes, which are not to be detected without some degree of discernment. The wren, which dwells in hedge-rows and thickets, commonly builds its nest of the moss in which it is accustomed to search for insects; but at times it departs from this custom, and employs feathers and hay, when they are to be had. The raven, which feeds on carrion, frequenting pasture-grounds and warrens, builds its nest of wool and fur; the lark builds in a furrow, employing dry twigs, interwoven with fine blades of grass, which it collects when looking for worms; the kingfisher uses the bones of fishes he has eaten. The long-legged and big-beaked flamingo, which stalks about in wet flats, builds a conical hillock of mud, and in this deposits her eggs, so as to sit easily upon them, and to keep them out of the water.
In what respect are these animals, which avail themselves of the circumstances around them for a perfectly determinate object, inferior to the Patagonian, who builds for himself a rude shelter of foliage; or to the African negro, who scoops out a hole in the ground? It will be said that man progresses: but that is not universally the case. What progress is shown in the palm-leaf huts of American savages, the tent of the Arab, the Irish mud-cabin, the stone hovel of the Scottish peasant, which appear to belong to primitive times? The art of house-building remains stationary, if it is in conformity with tastes and habits which are unalterable, because the physical conditions which determine them are ever the same. Sometimes even a habit once engendered persists, though the exterior conditions be changed. The Malays from time immemorial built their houses on piles, after the manner of the lacustrine dwellings of ancient Europe; and this mode of building has sunk so deep into the manners of tribes which have penetrated into the interior of the islands and settled on arid plains, or on rocky mountains, that they still go on prudently raising their houses above the surface of the ground. And yet, no one imagines that in these inveterate habits we have a case of instinct; and certainly no one would suppose that an Arab infant brought up in France would feel the need of dwelling in a tent of skins, or that a young Malay, if brought to Europe, would bring with him his habit of building on piles. The unvarying processes of barbarous tribes are