These fishes, however, are soon able to hold themselves in a vertical position, and no permanent effect is thus produced.

With the Pleuronectidae, on the other hand, the older they grow the more habitually they rest on one side, owing to the increasing flatness of their bodies, and a permanent effect is thus produced on the form of the head, and on the position of the eyes.

Judging from analogy, the tendency to distortion would no doubt be increased through the principle of inheritance.