1901.] on Colour in Amphibia. 591 



the best examples is the little North American Tree-frog (Hyla versi- 

 color^. It prefers to rest upon bark ; for instance that of an oak tree. 

 It is, as a rule, delicately silky-grey, with most variable dark mark- 

 ings. Sometimes the bark is suffused with a tint of green, so that it 

 is well-nigh impossible to discover the frog ; but when disturbed he 

 takes a tremendous leap. There is a flash of yellow or orange, due 

 to the suddenly-exposed flanks and inner sides of the legs, and he 

 is gone. He has dazzled his would-be captor by the display of unex- 

 pected colour. 



A third principle is that of Warning colours ; a combination of 

 bold patches, usually saturated yellow, orange or red, upon a black 

 background. All the Amphibia coloured thus are rather poisonous, 

 the venom being contained in the numerous glands of the skin, and, 

 although there are exceptions, they are practically safe from attacks. 

 The conspicuous pattern acts as a warning to the enemy. 



The combination of yellow and black in noxious creatures is a 

 widely dispersed principle. It applies to wasps, many butterflies and 

 moths ; and the only poisonous lizard, Heloderma, the Gila monster 

 of Mexico, is also black and orange. 



Several interesting facts are connected with these warning colours. 

 First, they are displayed upon those parts which are most exposed 

 during the ordinary attitude of the Amphibian, the colours being 

 intended to be seen. Secondly, the pattern is, as a rule, irregular, 

 instead of following the general law of being symmetrically disposed. 

 Lastly, they are subject to much individual variation. 



Examples are, the Fire-Salamander, so common on the Continent, 

 black, with yellow patches on the back ; several species of the genus 

 Spelerpes in North America. Many Newts, both in Europe and in 

 America, have the warning colour displayed upon the under parts, 

 e.g. Triton torosus of N.W. America and T. alpestris, the alpine 

 Newt of the Continent. The same principle, display of conspicuous 

 colours on the under surface, while the upper parts are inconspicuous, 

 occurs in many Frogs and Toads of the most widely separated parts of 

 the world. The reasonable explanation seems to be that these crea- 

 tures spend a great part of their time in the water. When swimming, 

 or suspended motionless in that element, their under surface is the 

 one which is most exposed to attack from other aquatic animals, as 

 fishes, water-tortoises, etc. An example is the little fire-bellied toad 

 of the Continent (Bombinator igneus). 



A third type of warning pattern is displayed by certain arboreal 

 frogs, which are conspicuous on both the under and upper parts, and 

 this pattern is irregular, asymmetrical, and, individually, variable, as 

 usual in poisonous Amphibia. The best example is the South American 

 genus Dendrobates, the poison of which is used by the South American 

 Indians in various ingenious ways ; for instance, poisoning of arrows 

 to shoot monkeys with, and dyeing of live parrots. 



To revert to the origin of the colour. We have already concluded 

 that a dominant factor in the production of colour is sunlight. The 



