When this great living bladder is emptied, the animal may be said to resemble a bag of gold-beaters' skin filled with bones. Chameleons exhibit great variation in their colours; that is to say, they may be almost white, sometimes yellowish, at other times green, reddish, and even black, either in portions, or all over their bodies. These changes of colour were for a long time attributed to the greater or less distention of the vast lungs they possess, and to the corresponding modifications in the quantity of blood sent to the skin; but this explanation is now abandoned. According to Mr. Milne Edwards, the cause of these variations of colour lie in the peculiar structure of their skin, in which there exists two layers of membranous pigment, placed the one above the other, but disposed in such a manner as to appear simultaneously under the cuticle, and at other times so that the one hides the other. Again, occasionally the cuticle is hidden under the superficial pigment. [Sixteen or seventeen species of Chameleon are described in the British Museum Catalogue. I. Having an erect fin on the back, the belly crested; which includes the Fringed Chameleon, _C. cristatus_, a native of Fernando Po. II. Having the back high, and compressed belly and sides, with a toothed crest; including the Side-crested Chameleon, _C. laterales_, a native of Madagascar. III. The back and belly having a toothed crest, the sides simple, the scales small and equal, muzzle simple; including the Common Chameleon, _C. vulgaris_, with many synonyms. It is a native of the East Indies, is the recognised type of the family (Fig. 32), and the one most commonly brought to England. There are probably two varieties,--one from North Africa, which is also found in Sicily and the South of Spain; the other, the East Indian variety--_C. Senegalensis_, the Senegal Chameleon, a native of West Africa; _C. arpelis_, from Ashantee and Gaboon; _C. verrucosus_, a native of Bourbon and Madagascar; the Rhinoceros Chameleon, _C. rhinoceroceratus_, also from Madagascar. IV. Having a toothed crest on the back, with the belly and sides simple, the chin and muzzle simple; including _C. tuberculiferus_, a native of South Africa; _C. cucullatus_, the Hooded Chameleon, a native of Madagascar; _C. nasutus_, having the chin simple, and the muzzle compressed, and _C. bifurcus_, having the muzzle in the male forked--both natives of Madagascar; _C. Tigris_, Seychille Islands; _C. ventralis_, from South Africa, and _C. pumilus_, from the Cape of Good Hope. [Illustration: Fig. 32.--Chameleo vulgaris.] V. Having back and belly without crest; including _C. Parsonii_, a native of Madagascar; and _C. Owenii_, the Three-horned Chameleon, from Fernando Po, and _C. Brookesianus_, an adult species, from S. W. Brookes's collection. EMYDOSAURIANS