[Metameric components of the occipital region of the polypterids (Pisces)].

Investigations into the development of the pronephros in Polypterus senegalus senegalus Cuvier have shown several details on the composition of the occipital region of this fish. It has been shown that the first six metotic metameres contribute to the structuring of the occipital region. These six metameres also are responsible for the existence of the pronephros. The epimeres of metamere I atrophies in the beginning of larval life. The muscular structures derived from the four following metameres become englobed in the occipital region. In the myoseptum between the previous metameres V and VI the post-occipital semi-vertebra, a pecularity of Polypterus, arises. The first vertebra of the column arises between structures that are derived from the previous metameres VI and VII. Such statements have been possible by a close examination of the disposition of the pectoral fin nerves in several larval stages. Because these nerves have been labelled with different names in several studies, a comparison of these names has been necessary.