ENDOCRINOLOGY, REGENERATION AND MATURATION IN NEREIS

¹ Department of Zoology, University of Bristol, England

Normal and regenerative growth are partially separated from maturation, since during the later stages of maturation, growth does not occur. A mature animal almost invariably regenerates a pygidium but rarely regenerates segmental rudiments. The supraesophageal ganglion of a mature animal secretes less hormone than that of an immature animal, though it still induces a significant amount of regeneration when implanted into an immature, decerebrate host. The rate of secretion of such a ganglion is as great during the first five days after implantation into the host as it is subsequently. A single ganglion from an immature donor (in which it is known to be actively secreting) induces no regeneration when implanted into a mature host. Immature grafts, from which posterior segments have been removed, engage in virtually no segment regeneration when stitched into mature hosts. However, implantation of three ganglia removed from immature donors into each graft results in the formation of a significant but very small number of segmental rudiments in host and graft. These results suggest that there may be a feedback from the maturing body, inhibiting the secretory activity of the ganglion. They are consistent with the suggestion that a single hormone secreted by the supraesophageal ganglion in immature Nereis both inhibits maturation and promotes growth in intact and regenerating animals.