We have heard of blind fish, but here is one--called by the Indians
tralhote, and known to naturalists as the Anableps tetraophthalmus,
signifying "four-eyed"--possessing four eyes. A membraneous fold,
enclosing the bulb of the eye, stretches across the pupil, dividing the
visual apparatus into the upper and lower half; a curious formation,
suited to the peculiar habits of the anableps. These fishes gather in
shoals on the surface of the water, their heads resting partly above and
partly below the surface, and they move by a leaping motion somewhat
like that of frogs on land. Thus, half in and half out of the water,
they require eyes adapted for seeing in both elements, and the
arrangement described just meets this want.