THE PROCESS OF REGENERATION IN HYDROIDS

Abstract

Summary1. In the hydroids in general, and Tubularia and Corymorpha in particular, the stimulus for regeneration involves two factors: (1) removal of dominance exerted by either the fully formed hydranth or a regenerating hydranth, and (2) the presence of a gradient of oxygen at a localized region of the stem or a mass of cells isolated from the stem.2. Dominance, or the inhibitory effect of a regenerating region, can be explained either on the basis of electrical differences in potential which produce chemical inhibition, or as the competition of regions of the stem for hypothetical substances circulating in the stem and necessary for regeneration. As yet no single experiment has decided between these two explanations of dominance and both should be subjects for investigation.3. The regional differences in rate of regeneration are correlated with regional differences in the rate of oxygen consumption of the stem, and the rate of regeneration can be varied by varying the oxygen consumption of the stem. These regional differences in oxygen consumption are due to differences in the resting stem and are not caused by the regional differences in regeneration.4. Since the stimulus for regeneration can be traced to an oxygen gradient, which results in an oxygen consumption gradient in the tissues, there is little value in speaking of an organizer in hydranth formation. Any agent which will bring about the above conditions will be an organizer. It is, therefore, possible to speak of the following as organizers: (1) oxygen locally applied, (2) tissues that have a higher oxygen consumption than the surroundings, and, perhaps, (3) respiratory catalysts, when their effects are investigated. On the whole, it would be better to speak of the coenosarc as organizing itself in response to a stimulus. The manner in which the tissue responds by cell movements and change in form is, of course, entirely unknown.