M. Pouchet of Rouen proved that when the new streets of that city were erected, the window-swallows altered their nests and substantially improved them. A short account of his observations will be found in Wallace's _Contributions_, 228 A. Mr. Wallace adds several instances of bad nest building, especially by pigeons, rooks, and window-swallows, a circumstance also noticed by White of Selborne. Amongst the most remarkable bird-families with special ideas of construction, are the mound-builders, and bower birds of Australia, described by Mr. Gould. The former hatch their eggs in hillocks contrived to retain during the night, amid their warm vegetable linings, the solar heat of each successive day. The nests of one family are about a yard high and three wide. In another family, mounds of five yards in height and twelve in girth seem not uncommon; and the circumference of one mound in particular measured full fifty yards. These larger mounds are the work of many birds, through many years, and their firm sides are covered by ancient forest growth. The bower birds construct over-arching alleys of curved branches, decorated with pretty grasses, gay feathers, shells and bones, particularly near the entrances. These bowers seem to be used as meeting and recreation places for both sexes. They vary to some extent amongst the different species of this singular tribe. There can be no doubt of the power of adaptation among animals;--and those who study them most are least surprised at its extent. Horses will learn to go up and down stairs, cats to undo door latches; and one pony mentioned by Jesse used to unfasten the stable door, open and rob the corn chest. Still more curious, is the American bird called _neuntödter_, which catches grasshoppers and spears them upon twigs, not for the shamble-purposes of the butcher bird, but simply as baits to catch and eat the smaller birds attracted by the spoil. Schleiden (_Plant_ 232), tells a most singular story of a Kangaroo who tried to drown his pursuer, and shewed considerable craft in the way he set about the drowning. After knocking the hunter backwards into a pond, the "old man" (Australian for Kangaroo) kept pushing the poor fellow's head under water every time he raised it up. If Kangaroo had never drowned a human being before, he must have proceeded by analogy, and argued, as some Naturalists do, from the brute to the man. A dog, mentioned by Jesse, endeavoured to save his drowning master's life by the reverse process to Kangaroo's, and would not let the beloved head disappear under water for many a wintry hour after life had been extinguished. (_Country Life_, p. 119.)