S6 REPTILES 



name from the green colour characteristic of the group in 

 general. Seeing that these snakes are nearly allied to the 

 American Herpetodryas, it would be rash to affirm, despite 

 their wide geographical separation, that their green livery has 

 been independently acquired. Whatever doubt may exist in 

 this case, it is practically certain that the arboreal Indian 

 whip-snakes (Dryophis) and their American and Malagasy re- 

 latives of the genus Philodryas have developed their green 

 colour apart from the members of the above-mentioned groups. 

 For these snakes belong to a section of the Colubridce in which 

 the hind teeth in the upper jaw are grooved for carrying poison, 

 whereas those of Herpetodryas, Dendrophis> etc., are solid ; — a 

 difference implying a widely sundered ancestry. The long and 

 slender bright green whip-snakes are almost impossible to detect 

 when among the foliage of their native forests, and are even 

 difficult to see when coiled among the branches of a small shrub 

 in captivity. One species of viper {Lachcsis wagleri) of the 

 Malay countries is also bright grass-green in the young state, 

 although later on the scales develop black edges, and in the 

 adult condition the whole colour becomes blackish. This viper 

 has a prehensile tail and feeds largely on birds, and is thus to a 

 great extent arboreal. That the green colour in the young is 

 protective and has been developed independently from that of 

 all the colubrine tree-snakes is manifest ; but why the creature 

 should turn black in old age is a puzzle. Possibly the adult 

 may lie more on the larger boughs than the young. 



Many desert snakes present a remarkable protective resem- 

 blance to their surroundings. In no case is this more pro- 

 nounced than in the horned viper (Cerastes cornutus) of 

 North-eastern Africa and Arabia, which is sandy coloured, and 

 in the day-time is in the habit of lying buried in the sand with 

 only the eyes, nostrils and the horn-like processes on the head 

 exposed, when it is practically invisible. The European rhino- 

 ceros-viper {Vipera ammodytes) presents a similar intimate re- 

 semblance to its desert surroundings. Although conspicuous 

 when removed from its natural surroundings, the Cape puff- 

 adder ( Bitis arietans\ with its yellowish or orange-brown 

 ground-colour marked by chevron-shaped dark barrings, is 

 almost invisible when on sandy and stony ground. 



The last instance of protective coloration among snakes to 



