It is obvious that unless the lower eye did thus travel round, it could not be used by the fish while lying in its habitual position on one side.

The lower eye would, also, have been liable to be abraded by the sandy bottom.

That the Pleuronectidae are admirably adapted by their flattened and asymmetrical structure for their habits of life, is manifest from several species, such as soles, flounders, etc.

, being extremely common.