Ab looked and, in an instant, realized how wise had been Oak's alarming cry and how well it was for them that they were so distant from the clump of trees so near the river. What he saw was that which would have made the boys' fathers flee as swiftly had they been in their children's place. Yet what Ab looked upon was only a waving, in sinuous regularity, of the rushes between the tree clump and the river and the lifting of a head some ten or fifteen feet above the reed-tops. What had so alarmed the boys was what would have disturbed a whole tribe of their kinsmen, even though they had chanced to be assembled, armed to the teeth with such weapons as they then possessed. What they saw was not of the common. Very rarely indeed, along the Thames, had occurred such an invasion. The father of Oak had never seen the thing at all, and the father of Ab had seen it but once, and that many years before. It was the great serpent of the seas! Safely concealed in the branches of a tree overlooking the little valley, the boys soon recovered their normal breathing capacity and were able to converse again. Not more than a couple of minutes, at the utmost, had passed between their departure from their place of labor and their establishment in this same tree. The creature which had so alarmed them was still gliding swiftly across the morass between the lowland and the river. It came forward through the marsh undeviatingly toward the tree clump, the tall reeds quivering as it passed, but its approach indicated by no sound or other token of disturbance. The slight bank reached, there was uplifted a great serpent head, and then, without hesitation, the monster swept forward to the trees and soon hung dangling from the branches of the largest one, its great coils twined loosely about trunk and limb, its head swinging gently back and forth just below the lower branch. It was a serpent at least sixty feet in length, and two feet or more in breadth at its huge middle. It was queerly but not brilliantly spotted, and its head was very nearly that of the anaconda of to-day. Already the sea-serpent had become amphibious. It had already acquired the knowledge it has transmitted to the anaconda, that it might leave the stream, and, from some vantage point upon the shore, find more surely a victim than in the waters of the sea or river. This monster serpent was but waiting for the advent of any land animal, save perhaps those so great as the mammoth or the great elk, or, possibly, even the cave bear or the cave tiger. The mammoth was, of course, an impossibility, even to the sea-serpent. The elk, with its size and vast antlers, was, to put it at the mildest, a perplexing thing to swallow. The rhinoceros was dangerous, and as for the cave bear and the cave tiger, they were uncomfortable customers for anything alive. But there were the cattle, the aurochs and the urus, and the little horses and deer, and wild hog and a score of other creatures which, in the estimation of the