26 INTRODUCTION. 



lenta have shown that the changes are controlled 

 by the animal, the contraction or expansion of the 

 chromatophores not being due entirely to the direct 

 action of light and moisture upon the skin, but also to 

 a reflex action of the sympathetic nervous system 

 brought about by the visual impression. Comparative 

 experiments conducted on frogs possessed or deprived 

 of the sense of sight, and placed in different conditions 

 of light, show the blind individuals to change colour 

 much less rapidly. 



The changes which we observe in Hyld, Rana, and 

 Bitfo are not limited to the ground colour, but also 

 extend to the markings. The tree-frog, normally 

 uniform, may become covered with lighter or darker 

 dots or spots, sometimes disposed with great regu- 

 larity and even assuming the form of cross-bars on 

 the limbs. An edible frog, of a fine grass-green with 

 few black spots above and with a pure white belly 

 when captured, may shortly after, when transferred to 

 an aquarium, appear largely marbled with black both 

 above and beneath. 



F. Werner has proposed to group the European 

 Batrachians, with respect to this peculiarity, into 

 such as actually change colour {Alytes, Hyla, Bufo, 

 Ra i ia), and such as only lighten or darken their shade 

 (DisGoglossus, Pelodytes, Pelobates). He considers 

 Bombinator as representing a third category, no 

 changes of any kind taking place ; but I cannot agree 

 with him in this, as I have seen B. pachypus pass 

 from yellowish to a very dark brown, and also vary in 

 the presence, absence, or distinctness of the light and 

 dark markings. 



In a recent work on East African Reptiles and 

 Batrachians G. Tornier endeavours to show that the 

 yellow and red pigments do not exist as chemical 

 entities, but are only degenerations of the brown 

 pigment or " melanin." And as a first " simple and 

 sure " proof of his contention he adduces the example 

 of Pelobates fuscus larvas, which according to him are 



