Introduction 



of all these facts gives us some understanding of the astonishing 

 changes and combinations of colours seen in some of the North 

 American tree frogs, such as Hyla regilla. 



As a rule, the colouration of the Tailless Batrachia is seldom 

 plain green or brown but is more or less spotted, mottled, or 

 striped, so that the animal blends with the detail of its background 

 and is more or less invisible. There are no Salientia in North 

 America that, like some of the black and yellow salamanders, 

 present sharp contrast of striking colours, and so warn their neigh- 

 bours of their poisonous character. 



Broadly speaking, the lower Families have less complex pig- 

 mentation and skin structure than the higher forms, so that 

 their colours are likely to be greys, browns, and olives, with some 

 admixture of red and yellow. This is true of the Discoglossidae, 

 Pelobatidae, and Bufonidae. The most complex colouration is 

 possessed by the Hylidae and Ranidae. With exceptions, they 

 have the interference layer well developed, and so are brown or 

 green, changing from one to the other and through many shades 

 of each, besides having^additional effects produced by red, white, 

 and metallic pigments. Of the Ranidae, Rana palustns, sylvatica, 

 and virgatipes represent some of the species that, as far as ob- 

 served, are never green ; catesbiana, grylio, clamiians, and pipiens 

 are among those that change rapidly from green to brown. 



The colours of the upper parts of the frog or toad make it 

 harmonize with its surroundings. Many Hylidae and Ranidae 

 have bright colours on portions of the body concealed during 

 rest, but displayed in leaping and swimming: witness the orange 

 yellow of Hyla versicolor, Hyla andersonii, and Rana palusiris, 

 and the bright red of Rana draytonii, as well as of Rana pretiosa 

 and Rana aurora of the Pacific Slope. These brilliant colours are 

 called flash colours. 1 They may act as recognition marks for 

 others of the same species, or may serve to startle the enemy and 

 warn of the more or less poisonous character of the possessor. 



The colour patterns of the Salientia are interesting when 

 we consider their origin in past ages. They have come into ex- 

 istence slowly, through the influence of light, and probably as a 

 direct result of the alternating spots and bars of sunshine and 

 shadow cast on the creatures by the sun shining through the 

 foliage of their environment. The pigment was gradually mar- 



1 Hans Gadow, Cambridge, England. 



26 



