CHAPTER II 

 THE FROG RANA TEMPORARIA 



Introduction General Internal Structure Skeletal System Muscular 

 System and Integument. 



Introduction. 



Few four-legged animals are more common or more readily 

 obtained than the common grass frog, Rana temporaria. It is to be 

 found in the damp grass in the neighbourhood of ponds and ditches 

 in all parts of the British Isles, and is probably the only native frog. 

 A larger form. Rana esculenta, the edible frog, is very abundant on 

 the continent, and although rare in this country is not infrequently 

 imported by dealers, and finds its way thence into the laboratory. 

 For our purposes the differences, in the main of size and colour, 

 between the two species need not be taken into account. 



The colour of the grass frog is subject to great variation, according 

 to the nature of the surroundings in which the animal lives, but 

 generally the back is mottled dark green, brown and black, and the 

 under surface is pale yellow with a few dark spots. The coloration 

 is due to the presence in the skin of a large number of deeply 

 pigmented cells, and the colour of an individual can be changed to 

 suit its habitat by an alteration in the size of the coloured cells. 

 They can each be contracted into quite a tiny spot or, again, spread 

 out over a comparatively large area. In this way the frog is 

 protected from its enemies, for it is able to harmonise with the ground 

 and so escape detection as long as it remains still. It is almost 

 equally at home on the land or in the water, and it belongs to that 

 class of animals termed the AMPHIBIA, in order to indicate this 

 capability of living either aquatic or terrestrial lives. Although 

 unable to walk easily it can still get about well on land, and in the 

 water is a powerful swimmer. The long hind legs serve as efficient 

 swimming organs, and also for locomotion on land by means of a 

 series of jumps. It moves freely from place to place, and so we say 

 it exhibits the power of voluntary movement. The food of the frog 



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