CHAPTER IX. 



THE FROG (RANA TEMPORARTA AND RANA ESCULENTA). 



This country is inhabited by two species of Frog. One, Rana 

 temporaria, is abundant everywhere — where, that is to say, 

 suitable conditions are to be met with. The other frog, Rana 

 esculenta, the so-called " edible frog " (but both, as a matter of 

 fact, are eaten), is found in some of the eastern counties. 

 There is, however, more than one reason for regarding this 

 species as not truly indigenous 

 to this country; it has been 

 artificially introduced at more 

 than one time. 



R. esculenta may be distin- 

 guished from R. temporaria 

 by the existence in the male 

 of inflatable vocal sacs, by the 

 absence of a characteristic dark 

 patch of pigment behind the 

 eye, and by the larger prehal- 

 lux in the foot. It is, moreover, a larger species, and is more 

 purely aquatic in habit than its smaller indigenous ally. 



The frog varies considerably in colour, being in some cases 

 darker and in others lighter. This variation of colour is de- 

 pendent largely upon the animal's surroundings, and changes 

 with any changes in the environment. Thus, if a frog be kept 

 for some time in a white dish it will become paler in tint ; if 

 shaded, the hues will darken. This power of changing the 

 colour is due to the contraction or relaxing of certain pigment- 

 cells in the skin, and is a phenomenon which is common among 



Fig. 33. — The upper side of the head of the 

 male Rana esc7tlenta, showing the vocal 

 sacs inflated. 



