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340 fore limb of the former, we may perhaps surmise, was of so small a size that, even after it had become fin-like, only those variations in the direction of smallness were of benefit to it, whereas, for a contrary reason, the reverse was the case with the other—though I should think this far more likely if the true seals, like the beaver and otter, had a large and well-developed tail. As they have none, I rather suppose that their fore-feet were, for some period, enlarged and broadened out, and only ceased to be so owing to the gradual tail-like development of the hind feet and posterior part of the body. This, the evolved tail, began then to play the chief part in natation, as it does in fishes, and, for similar reasons, I believe that the otariidæ are advancing along the same lines, and that their mode of progression in the water will, one day, be more truly seal-like—that is to say, fish-like—than it is at present.

But let the ancestry and process of modification, as between the two families, have been as different as we can, with any likelihood, suppose it to have been, yet still it is not quite easy to understand why one marine animal should, whilst retaining the power of quadrupedal progression, possess also greater aquatic powers than another one, which, travelling by the same evolutionary road, has gone farther on it, has lost the terrestrial gait, become less a quadruped, and approached considerably nearer to the true aquatic, or fish, type. Should not the fish form excel all other forms in the water? and, if so, should not the