123 REPTILES AND BIRDS. 
some spaces are left free, into which the air penetrates, causing the 
skin to expand ; this mechanism is voluntary, the animal having the 
power of inflating or relaxing it at pleasure. 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 distension 
of the vast lungs they possess, and to the corresponding modifications 
Pig. 31.—Common Chameleon. 
in the quantity of blood sent to the skin; but this explanation is now 
abandoned. According to M. 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, or at other times to contract 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. er7status, a native of Fernando Po. 
