560 



AMPHIBIA. 



THE FROG AS A TYPE OF AMPHIBIANS. 



The common British frog (Rana tewporarid] and the 

 frequently imported continental species (R. esculenta) agree 

 in essential features. 



Though aquatic in youth, they often live in dry places, 

 hiding in great drought, reappearing when the rain returns. 

 Everyone knows how they sit with humped back, how they 

 leap, how they swim. They feed on living insects and slugs. 

 These are caught by the large viscid tongue, which, being 



FIG. 271. The Edible Frog (Rana esculenta}. 



fixed in front of the mouth and free behind, can be jerked 

 out to some distance, and with even greater rapidity re- 

 tracted. When a frog is breathing the nostrils are alternately 

 opened and closed, the under side of the throat is 

 rhythmically expanded and compressed, the mouth re- 

 mains shut meanwhile. The males trumpet in the 

 early spring to their feebly responsive mates. In our 

 British species the pairing takes place soon after; the 

 young are familiarly known as tadpoles, and a notable 

 metamorphosis takes place. In winter the frogs hiber- 

 nate buried in the mud of the ditches and ponds, mouth 



