COLORATION AND ITS INTERPRETATION 85 



like tree-frogs ; and their changes in colour are very rapid in a 

 state of nature. 



Other tropical American lizards belonging to the family 

 Teiidce, or tejus, and the genus Ameiva, also possess the power 

 of changing colour, although apparently to a more limited ex- 

 tent ; and in this case also the power seems to have been inde- 

 pendently acquired. A fourth instance of a similar colour- 

 change occurs in the Indian and Malay variable-lizard {Cal- 

 otes versicolor) ; and since this species is a member of the 

 family Agamida', which has no near relationship with iguanas 

 or tejus, the independent origin of the phenomenon may be 

 considered as beyond doubt. These lizards, which in the Malay 

 Peninsula are miscalled chairueleons by Europeans, are arboreal 

 and pugnacious in their habits. The normal colour of the skin 

 of the body is brownish, but when the lizard is feeding or ex- 

 cited this changes to pale yellow, while the head and neck be- 

 come suffused with brilliant red. When the male is courting 

 the female its hue becomes yellowish flesh-colour, with a con- 

 spicuous dark patch (which completely disappears when he is 

 disturbed) on each of the throat-pouches. 



As already mentioned, the coloration of a large number of 

 snakes (including pythons and boas) appears to be of a pro- 

 tective nature, but only a k\v instances of special adaptation of 

 this kind can claim notice. Among these, reference may be 

 made to the occurrence of a green colour, to harmonise with 

 their leafy environment, in several groups of those reptiles, 

 as there appears to be evidence that this has been acquired in- 

 dependently in at least two of these groups. The American 

 wood-snakes of the genus Herpetodryas, which belong to the 

 typical subfamily of the great family of Colubridtc, are purely 

 arboreal, and typically of a more or less uniformly olive-green 

 tone of colour. The sipo, or Brazilian wood-snake {H. cari- 

 jiatus), for instance, is normally bright verditer or olive-green 

 above, with a tinge of brown on the back, and greenish or 

 bright yellow below. Curiously enough, however, probably 

 owing to some difference in its habits — in the West Indies it 

 becomes blackish or blackish brown above, with the under parts 

 steel-grey. Nearly allied are the Old World and Australian 

 tree-snakes of the genera Dendrophis, Dendrelaphis and Chlor- 

 op/u's, the latter of which is confined to Africa and takes its 



