556 ANATOMY OF VERTEBRATES. 



pigmental system of the skin is remarkably developed in this 

 family : it is of various colours — red, blue, yellow, brown ; each 

 colour is lodged in contractile areolar spaces, and can be accu- 

 mulated near or withdrawn from the surface. When the Chame- 

 leon is kept long in a cold dark place all the pigment subsides 

 into the derm, the superficial pale grey colour of which appears 

 throvigli the thin epiderm. When brought into the light and 

 warmth the pigments flow to the surface, in harmony with the 

 colour of that on which the animal rests, which usually in this 

 arboreal reptile is green. If, however, the Chameleon be irri- 

 tated, the colour may change to a vinous red, or deepen almost to 

 black : commonly the surface is more or less mottled, grey, yellow 

 and green. These phenomena, which have made a proverb of 

 the Chameleon, are manifested in a minor degree by some other 

 lleptiles, by most Fishes, and by Cephalopods. 



The integument, besides covering the surface of the body, 

 extends, in many Lacertians, from various parts, in different 

 forms and degrees. In Basiliscus and Histiurus calotes it forms a 

 compressed fold or crest along the midline of the back and tail. 

 In Crocodilnrus the tail has a double crest above : in PhjUurus 

 platurus the lateral expansions of the skin of the short tail give it 

 a leaf-shape. In Hoplurus and Tropidurus cyclura the skin of the 

 throat is folded transversely : in Agama the transverse fold is asso- 

 ciated with a longitudinal fold beneath the under jaw. The jugular 

 fold is longitudinal and pendulous, like a dewlap, in Iguana, 

 Corythophanes, and SemiopJwrus. In Chlamydosaurus a very 

 broad transverse fold of skin extends from above each tympanum 

 across the lower part of the neck : it is partly supported and 

 moved by much elongated cerato- and thyro-hyals, and can be 

 expanded and brought forward or erected, so as to give a formid- 

 able aspect to this Lizard, when it is attacked or alarmed. 



In the small insectivorous Draco volans of Linnaius a broad 

 fold of skin, on each side of the body, fig. 163, is supported by 

 five pairs of slender elongated free ribs, fig. 50, by the movement 

 of which the folds can be expanded into a sort of parachute, as 

 explained at p. 265. The special modification of the tegument 

 of the toes in the Geckos is described at p. 263, fig. 162. In 

 the extinct Ptcrodactyles still more extensive duplicatures of skiu 

 were supported on a much elongated digit, and constituted true 

 wings, as in the Bats, p. 265, fig. Ill, a. In many Lizards, on 

 the inside of the thigh, there is a row of tubcrculate perforated 

 scales, beneath each of which lies a pedunculate gland, studded 

 with marginal follicles: the presence and position "of these ' pori 



