EARLY DEVELOPMENT AND ORGANIZATION OF THE RETINOPETAL SYSTEM IN THE LARVAL SEA LAMPREY, PETROMYZON-MARINUS L - AN HRP STUDY

Development of the retinopetal system of the larval sea lamprey, Petro myzon marinus, was investigated following labelling of this system by injection of horseradish peroxidase into the orbit. This study extends our previous report on larval stages and provides a detailed descript ion of the development of this system. We present quantitative and qua litative evidence suggesting that the retinopetal nuclei of Schober's M2-M5 nucleus, the mesencephalic reticular area and the tectum arise s equentially in that order, that the three-retinopetal nuclei originate from a common anlage in the ventricular zone of the mesencephalic teg mentum and that the retinopetal cell population increases throughout t he larval period. No neuronal death was observed. We also describe and discuss the significance of a transitory phase of retinopetal cell di fferentiation characterized by the presence of ventricular dendrites. Finally, we compare the development of retinopetal and retinofugal sys tems.