Studies on hydroid differentiation. III. The replacement of hypostomal gland cells of Podocoryne carnea

Pulse labeling with tritiated thymidine has permitted the identification of a progenitor cell compartment at the base of the hypostomal glandular ridges of the marine hydroid Podocoryne carnea. This progenitor compartment produces cells which move out on the ridges differentiate as digestive gland cells, and are ejected into the gastro‐vascular cavity. Spherous gland cells of the body appear not to be part of this circumscribed replacement system. There appears to be no proximal movement of gastrodermal cells in the body of this marine hydroid.