CHAPTER I 



THE COMMON FROG-RANA TEMPORARIA AND 

 RANA ESCULENTA 



THE frog commonly found in pools and ditches in England 

 is the brown or grass-frog, Rana temporaria. A larger 

 form, more abundant on the Continent than in England, is 

 known as the edible frog, Rana esculenta. A third species, 

 intermediate between the two, has been distinguished under 

 the name Rana oxyrhinus. The differences between these 

 three common species of European frogs are unimportant, and 

 may be neglected at this stage of our studies. 



In a frog belonging to any of these species the following 

 external characters may be noted without dissection. The 

 body is divisible into two regions, the head and trunk. 

 There is no neck, the head passing without any distinct break 

 into the trunk. There is no tail. P'urther, we may recognise 

 sides and surfaces which correspond to those of our own 

 bodies and are similarly named. There is an upper surface, 

 corresponding with our back, which we shall call the dorsal 

 surface ; an under side or ventral surface ; an anterior end 

 which indicates the direction in which the animal moves, and 

 a posterior end opposite to it. The attachments of the two 

 pairs of limbs mark the right and left sides of the body. 



The whole surface of the body is covered by a smooth 

 moist skin of a greenish yellow hue, mottled on the dorsal 

 surface with dark, almost black patches. The ventral surface 

 is generally yellow. 



Frogs have the power of varying their colour within certain 

 limits, so that the same specimen may present very different 

 appearances under different circumstances. The changes of 

 colour enable the frog to approximate its colour to that of 

 surrounding objects, and thus to conceal itself in some measure 

 from its enemies. The mechanism by which the changes are 

 effected lies in the structure of the pigment bodies of the skin, 



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