The pond on the moor is frozen over. What an epoch in the history of all its inhabitants! For they are not mostly long-lived creatures, these pond-dwellers; a summer forms an appreciable part of their short existence. Theirs is but a precarious life at the best of times; they have always to steer close between the Scylla of drought and the Charybdis of freezing. Half their days are spent in enforced seclusion. In the summer the pond, which is their universe, is apt to dry up and fail them; in winter it stands its even chance of freezing solid and entombing them. To meet these two extreme contingencies, all the world of the pond has had to accommodate itself to the possible chances of its fickle environment. The newts, for example, come here to breed every spring. They must needs do so, indeed, because their young have gills like a salmon or a herring, and can only breathe in their earlier stages the diffuse oxygen held in suspension in water. Newts, in fact, start in life as fish, but develop, half-way through, into lizard-like animals with lungs and legs, because of the annual drying up of their native waters. All higher life, indeed, was originally aquatic; it is only just because ponds dry up in summer that the ancestors of beasts and birds and reptiles ever ventured on dry land, at first for a brief excursion, and afterwards for a permanence. We are all in the last resort the descendants of amphibians. There are two kinds of newt in this pond, each with its own peculiar plan for meeting the difficulty of winter quarters. The great crested newt, who is the most confirmed water-haunter of the two, retires to the mud at the bottom of the pond in late autumn, and there lies torpid as long as the frost lasts, returning to the surface to breathe when the weather improves again. But the smaller newt, a more adventurous soul, goes ashore in summer, when the pond dries up, and stops there for the winter, lurking in long grass at the bottoms of ditches, or hiding in caves and damp vaults or cellars.

There are no fish in the pond, of course, because it is not permanent; it dries up in August. But there are frogs and tadpoles by the thousand in due season; and, what is odder still, the frogs are there now, though you cannot see them. Indeed, frogs and newts are merely slight variations on the fishy type, evolved to meet this very want and to fill this very place in the economy of nature: practically speaking, they are fish which turn at last into terrestrial reptiles. During the earlier spring days, when the ponds are full, the parents lay their spawn among the sunk leaves of water-weeds; and soon the tadpoles emerge from their jelly-like eggs, and swarm at the edge in a seething black mass of bustling and jostling life. Then, as the pond gets low, and breathing becomes difficult, they proceed by degrees to drop their gills, and develop the rudimentary swim-bladder into a pair of true lungs. Soon four weak little legs with sprawling fingers bud out at their sides; and, hi, presto! they hop or crawl ashore as full-fledged air-breathers. At this point grave differe............