From very ancient times the curious changes of colour which take place in the chameleon, and its supposed power of living on air, have been the wonder of the uninformed, and have furnished philosophers and poets with abundant material for metaphor. The belief that the animal can live on air has been exploded long ago, and was no doubt due to its power of long fasting and to its peculiar manner of breathing. It is only quite lately, however, that any satisfactory explanation has been given of the apparently capricious changes which take place in the colour of the chameleon; the latest researches on the subject being those of M. Paul Bert, the French naturalist, which have been described in a recent paper by M. E. Oustalet. As most of our readers are no doubt familiar with the appearance and figure of this curious reptile, and as descriptions of it may be found in any encyclopædia or elementary work on natural history, we do not consider it necessary to repeat them here.
Many and various theories have been proposed to explain the changes of colour which chameleons undergo; changes the importance of which have been greatly exaggerated. It is generally believed that these animals have the power of assuming in a few seconds the colour of any neighbouring object, and that they intentionally make use of this trick to escape more easily from the sight of their enemies. But this opinion is erroneous; and experiments conducted with the greatest care have proved that chameleons are incapable of modifying their external appearance in anything like so rapid and complete a manner.
The first probably to give any rational account of the causes of the puzzling changes of colour in these reptiles was the celebrated French naturalist, Milne-Edwards, about forty years ago. After a patient and minute examination, he discovered that the colouring matters of the skin, the pigments, are not confined as in mammals and birds, to the deep layer of the epidermis, but are partly distributed on the surface of the dermis or true skin, partly located more deeply, and stored in a series of little cells or bags of very peculiar formation. These colour-cells are capable of being shifted in position. When they are brought close to the surface of the outer skin, they cause a definite hue or hues to become apparent; but by depressing the cells and causing them to disappear, the hues can be rendered paler, or may be altogether dispersed. It is noteworthy that the cuttlefishes change colour in a similar manner.