AMPHIBIANS. 215 



road so thickly covered with little frogs, that it is difficult 

 to avoid treading on them. Country people, noticing the 

 rain and the frogs simultaneously, jump to the conclusion 

 that both came from the same source hence their ac- 

 counts of " Showers of Frogs." When on land the Frog 

 progresses by leaps, while in the water it swims by 

 means of the hind-limbs alone. Although the adult Frog 

 is a lung-breather, it can remain a long time under water 

 without coming to the surface for air ; when it does 

 come up it may be seen to open its mouth, releasing 

 a large bubble of vitiated air which it had been retaining 

 all this time : it then takes in another mouthful of air, 

 closes its lips, and again dives down. In hot weather it 

 often thus spends hours in the water, although of course 

 it generally lives on land. As the skin is thin and very 

 permeable to fluids, there is no doubt that the blood 

 near its surface is largely aerated through it, as it is 

 through the gills in fishes and tadpoles. The eye, which 

 has a horizontal pupil, is furnished with eyelids, as in 

 lizards ; it has also a nictitating membrane. In winter 

 frogs collect together in masses in the mud at the bottom 

 of ponds, etc., " embracing each other so closely as to 

 appear almost one continuous mass." They remain thus 

 in a state of complete torpor, neither feeding nor breath- 

 ing unless through the skin as suggested above but 

 secure from injury, and beyond the reach of frosts: when 

 roused by the return of warmer weather in the spring, 

 they at once set about the important business of spawn- 

 ing, as detailed in the introduction to this chapter. The 

 epidermis, as we have seen, is colourless, but in the 

 under layers of the skin are numerous dark pigment cells 

 to which the colour is due. It has been noticed that the 



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