The perfectly-formed frog does not live of necessity in water, or near it, but requires damp air occasionally. It breathes by lungs, as we have said; but, as it has no ribs, there is no chest to heave mechanically. The frog's air has to be swallowed, to be gulped down into the lungs. That is not possible unless the mouth is shut; and, therefore, as we might suffocate a man by keeping his mouth shut, so we should suffocate a frog by keeping his mouth open. Yet we should not suffocate him instantly; we should disable the lungs; but, in this class of animals the whole skin is a breathing surface. A frog has lived a month after his lungs had been extracted. All respiratory surfaces, like the inside of our own lungs, can act only when they are relaxed and moist. That is the reason why a frog's skin is always moist, and why a frog requires moist air. It does not need this constantly, because, when moisture is abundant, there is a bag in which it stores up superfluity of water, to be used in any day of need. It is this water--pure and clear--which frogs or toads expel when they are alarmed by being handled. Is not enough said here, to rescue frogs from our contempt? We may add, that they are capable of understanding kindness--can be tamed. Frogs hybernate under the mud of ponds, where they lie close together, in a stratum, till the spring awakens them to a renewal of their lives and loves. They lay a vast number of eggs, at the bottom of the water; and the multitudes of young frogs that swarm upon the shore when their transformation is; complete, has given rise to many legends of a shower of frogs. These multitudes provide food for many animals, serpents, as we have seen, birds, fish. And the survivors are our friends. The other species of frog found in this country is the Edible Frog (_Rana esculenta_). It has for a long time had a colony in Foulmire Fen, in Cambridgeshire, although properly belonging to a continental race. It differs from our common frog in wanting a dark mark that runs from eye to shoulder, and in having, instead of it, a light mark--a streak--from head to tail along the centre of the back. The male is a more portentous croaker than our own familiar musicians, by virtue of an air-bladder on each cheek, into which air is forced, and in which it vibrates powerfully during the act of croaking. This kind of frog is always in or near the water, and being very timid, plunges out of sight if any one approaches.