Peripheral innervation by migrating neuroblasts in the chick embryo

Horseradish peroxidase (HRP) was injected into the mandibular process of the first visceral arch in chick embryos of 3-6 days of incubation. On days 3 1 2 , 4 and 4 1 2 of incubation, this procedure resulted in granular reaction product in neuroblasts of the lateral trigeminal nucleus and in soma and processes of neuroblasts in the process of migrating from the medial column to form the lateral nucleus. On days 5 and 6 of incubation, similar labeling was found in cells migrating from the lateral nucleus dorsal to form the dorsal trigeminal nucleus. This is the first clear demonstration of the extent of differentiation which may take place during neurogenesis prior to the completion of migration.