II.—The asymmetry, metamorphosis and origin of flat-fishes

Abstract

It is now a well-known fact that every Flat-fish begins life with the eyes in the normal position; the asymmetry of its skull is not born with it, but acquired during the early development. The conversion of a normal fish is thus a constant occurrence, year by year, and we should be able to determine the causes of the phenomenon. The normal condition may be taken for granted; the abnormal requires explanation. The adult asymmetry of a few forms is also known, but the descriptions are imperfect or incomplete. Each part has an asymmetry of its own, it is said; the frontals display torsion, the eyes have somehow come to one side of the head and the other parts have somehow altered and fitted themselves into the new conditions. No attempt has been made to correlate the changes in the different parts.