bercles, often ridged or spinous, always horny in texture, not bony: those of the head frequently take the form of many-sided plates, more or less large, and those of the belly are square and overlapping. The scales of the back are generally elevated into spinous processes, forming a saw-like crest, which runs down the back and tail in various degrees. The toes are always free, commonly slender; but in some genera, as Anolis, Dactyloa, &c., they have the dilated and lamellated tips of the Geckotidæ. These have the power of crawling with ease and rapidity on perpendicular surfaces, and haunt out-buildings, and even dwelling-houses in the hot parts of America and the West Indies, running with great agility about the walls, and leaping from place to place; while others run and leap with equal sprightliness among the twigs and leaves of low shrubs in pursuit of insects. These have the faculty of changing their colours, which is effected with a rapidity and to an extent scarcely inferior to what we see in the Chameleons. All the genera appear to be more or less arboreal; the larger species, or true Iguanas, living almost entirely on trees: these are reported to be able to swim with ease, but their feet do not manifest any structural adaptation to aquatic habits, and we doubt whether they ever take to the water except in an emergency, or impelled by some unusual motive.
Most of the species in this Family have some expansion of loose skin about the neck. In the Iguanas it hangs down in a permanent sort of dewlap, but in the Anoles it is ordinarily contracted and consequently invisible, but is ex-
