CHAPTER V.

MORPHOLOGY OF THE FINS OF FISHES.

Origin of the Fins of Fishes.--Origin of the Paired Fins.--Development of the Paired Fins in the Embryo.--Evidences of Palæontology.--Current Theories as to Origin of Paired Fin.--Balfour's Theory of the Lateral Fold.--Objections.--Objections to Gegenbaur's Theory.--Kerr's Theory of Modified External Gills.--Uncertain Conclusions.--Forms of the Tail in Fishes.--Homologies of the Pectoral Limb.--The Girdle in Fishes other than Dipnoans. 62