THE COLOR CHANGES OF FROGS. 491 



change their color to agree with the environment. The latter 

 method would, of course, from the frog's point of view, be decid- 

 edly the more desirable, saving him much exertion in seeking 

 safe retreats ; and recent researches have shown that this is in 

 fact the method adopted. 



The ability of the tree frogs, or "tree toads" (Hylidce), to 

 change their color has long been known, but precise studies of 

 the color changes of the common ground frogs (Ranidce) have 

 only been made com- 

 paratively recently, 

 and as yet the record 

 is far from complete. 

 A few years ago Dr. 

 Fickert, of Tubingen, 

 experimented with the 

 color adaptability of 

 the common European 

 frog (Rana tempora- 

 ria) : " Three frogs ap- 

 proximately similar in 

 color were placed in 

 three glass vessels, of 

 which the first stood 





on a black, the second FlG I ._ WOOD FROG . Adult . 



on a green, and the 



third on a white surface, being surrounded up to a height of some 

 five centimetres with the same color. After about an hour and 

 a half the frog a on the black surface was the darkest, b on the 

 white the lightest, while the frog c surrounded by green was in- 

 termediate in color between the two. Hereupon the frog a was 

 transferred to the glass on the white, frog b into the one on the 

 black surface. After three quarters of an hour they were again 

 examined, and a was the lightest, b the darkest. Then c and b 

 were interchanged, and in a quarter of an hour c was the darkest, 

 while b was intermediate in color between c and a. When, final- 

 ly, b and a were interchanged, a change of coloring appeared im- 

 mediately ; b became light again, and a took the intermediate tint 

 between b and c." * 



A similar but less complete experiment with the same species 

 of frog was made many years previously by Sir Joseph Lister, 

 who found that " a frog caught in a recess in a black rock was it- 

 self 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 hol- 



* Eimer, Organic Evolution, Cunningham's translation, p. 148. 



