ANALYSIS OF THE REGENERATIVE PROCESSES IN NEMERTEANS

¹ From the Osborn Zoölogical Laboratory, Yale University

1. An attempt to analyze the organizing potencies in the regeneration of fragments of the body in several species of nemerteans leads to the conclusion that the cut nerve cords liberate an agent which activates the dormant cells of the parenchyma and transforms them into regenerative cells. Bipolar migration of these cells leads to complete regeneration.

2. The different regenerative capacities in closely related species may be dependent upon differences in the extent of distribution either of this activating agent or of the regenerative cells. In one group the entire length of the body is included and all parts are equally capable of regeneration; in another group the regenerative potency reaches only to the middle of the foregut region, while in a third group of species it is limited to the anterior ends of the nerve cords and head-formation is limited to a single transverse plane.

3. The blastema is considered to be a self-determining system comparable to that of the early embryo. The constituent cells are evidently multipotent and capable of differentiation into any of the new organs. Once activated they and their descendants complete the regenerative processes.

4. The primary organization center is evidently associated with that part of the nerve cords which is capable of activating the regenerative cells and of controlling their bipolar migration. Secondary organization centers result as soon as the primordia of the organ systems have become differentiated in the self-determining blastema.