My acquaintanceship with tadpoles in the past had not aroused me to enthusiasm in the matter of their mental ability; as, for example, the inmates of the next aquarium to that of the Redfins, where I kept a herd or brood or school of Short-tailed Blacks--pollywogs of the Giant Toad (_Bufo marinus_). At earliest dawn they swam aimlessly about and mumbled; at high noon they mumbled and still swam; at midnight they refused to be otherwise occupied. It was possible to alarm them; but even while they fled they mumbled. In bodily form my Redfins were fish, but mentally they had advanced a little beyond the usual tadpole train of reactions, reaching forward toward the varied activities of the future amphibian. One noticeable thing was their segregation, whether in the mica pools, or in two other smaller ones near by, in which I found them. Each held a pure culture of Redfins, and I found that this was no accident, but aided and enforced by the tads themselves. Twice, while I watched them, I saw definite pursuit of an alien pollywog,--the larva of the Scarlet-thighed Leaf-walker (_Phyllobates inguinalis_),--which fled headlong. The second time the attack was so persistent that the lesser tadpole leaped from the water, wriggled its way to a damp heap of leaves, and slipped down between them. For tadpoles to take such action as this was as reasonable as for an orchid to push a fellow blossom aside on the approach of a fertilizing hawk-moth. This momentary co-operation, and the concerted elimination of the undesired tadpole, affected me as the thought of the first consciousness of power of synchronous rhythm coming to ape men: it seemed a spark of tadpole genius--an adumbration of possibilities which now would end in the dull consciousness of the future frog, but which might, in past ages, have been a vital link in the development of an ancestral Ereops. My Redfins were assuredly no common tadpoles, and an intolerant pollywog offers worthy research for the naturalist. Straining their medium of its opacity, I drew off the clayey liquid and replaced it with the clearer brown, wallaba-stained water of the Mazaruni; and thereafter all their doings, all their intimacies, were at my mercy. I felt as must have felt the first aviator who flew unheralded over an oriental city, with its patios and house-roofs spread naked beneath him.