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.

The chief advantages thus gained seem to be protection from their enemies, and facility for feeding on the ground.

The different members, however, of the family present, as Schiodte remarks, "a long series of forms exhibiting a gradual transition from Hippoglossus pinguis, which does not in any considerable degree alter the shape in which it leaves the ovum, to the soles, which are entirely thrown to one side." Mr.Mivart has taken up this case, and remarks that a sudden spontaneous transformation in the position of the eyes is hardly conceivable, in which I quite agree with him.