The capacity of the neural crest cells to differentiate into medullary cells of the adrenal gland has been tested for different levels of the cephalo-caudal axis of the chick embryo and at different stages.
The procedure consisted in associating a fragment of neural crest cells containing spinal cord with a section of an embryo containing the prospective cortical territory. The latter was previously deprived in ovo of presumptive medullar adrenal cells by localized X-irradiation of its spinal cord.
The portion of the spinal cord which has the capacity to give off medulloblasts is located not only within the prospective adrenal area (somite levels 18–22), but also within a region extending over a length of six somites in front and seven somites behind the presumptive zone.
This capacity, which is restricted in space, is also limited in time. It is possessed by the portion of spinal cord defined above from 6 h before the migration of the first neural crest cells and lasts roughly for 24 h after the beginning of migration. Furthermore, the experiments indicate that the differentiation of neural crest cells into medullocytes requires the inductive influence of the cortical cells.