IX. The development of the chondrocranium of the eel (anguilla vulgaris), with observations on the comparative morphology and development of the chondrocranium in bony fishes

This paper furnishes descriptions of certain stages in the development of the chondrocranium of the Common Eel (Anguilla vulgaris , Turton), and, in addition, provides a comparative account of the chondrocranial development in Bony Fishes, and particularly in the Teleosts. Since the publication of Hertwig’s treatise on comparative vertebrate embryology in 1906, in which the section dealing with the cranial skeleton was written by the late Prof. Gaupp, no adequate comparative study of the fish chondrocranium has been undertaken; in view of the fact that our knowledge of the subject has been considerably augmented in recent years, an endeavour to supply this deficiency seemed desirable. Owing to the limited time at my disposal, and the probability of the investigation being prolonged indefinitely, this comparative investigation is far from complete. In planning out the paper it was found convenient first to describe the development of the chondrocranium inAnguila , and to postpone the discussion and interpretation of the results to the latter part of the paper. The stages here described extend to the metamorphosis of the larvalLeptocephalus , at which time the chondrocranium has attained its maximum development. Certain observations on the later stages are recorded, in so far as they affect the interpretation or ultimate fate of the cartilaginous parts of the skull; it is hoped to describe these stages in greater detail, and to deal with the changes which lead to the formation of the adult skull in a subsequent paper.