The Dawn of Reason

One of the immutable laws of nature declares that animals which are placed in new surroundings, not fatal to life, undergo certain changes and modifications in their anatomical and physiological structures to meet the exigencies demanded by such a modification of surroundings. Thus, the flounder and his congeners, the turbot, the plaice, the sole, etc., were, centuries and centuries ago, two-sided fishes, swimming upright, after the manner of the perch, the bass, and the salmon, with eyes arranged one on each side of the head. From upright fishes, swimming, probably, close to the surface of the sea, they became dwellers on its bottom, and, in order to hide themselves more effectually from their enemies or their prey, they acquired the habit of swimming with one side next to the ground, and of partially or wholly burying themselves in the mud, always, however, with one side down.