VAEIABLE RESEMBLANCE IN VERTEBRATA, ETC. 83 



man knows that he stands an extra chance of catch- 

 ing his fish while the bait remains unadapted to its 

 environment. This experience serves to prove in a 

 practical way that the power of changing the colour is 

 essentially protective. 



Variable Protective Resemblance in Amphibia 



Other animals possess the same power. The Com- 

 mon Frog (Rana temporaria) can change its tints to a 

 considerable extent. Thus Sir Joseph Lister states 

 that ' a frog caught in a recess in a black rock was 

 itself almost black; but after it had been kept for 

 about an hour on white flagstones in the sun, was 

 found to be dusky yellow with dark spots here and 

 there. It was then placed again in the hollow of the 

 rock, and in a quarter of an hour had resumed its 

 former darkness. These effects are independent of 

 changes of temperature . . .' l The Green Tree Frog 

 (Hyla arborea), so common in the South of Europe, 

 is bright green when seated among green leaves, but 

 becomes dark-brown when resting on the earth or 

 among brown leaves. It is very interesting to notice 

 that when this frog turns brown, irregular spots 

 become conspicuous upon its skin, spots which evi- 

 dently correspond to those upon the Common Frog 

 (Rana), but which are invisible when the green tint is 

 assumed. 



1 Lister : Phil. Trans., 1858, vol. 148, p. 628. 



