1. A method has been devised for studying the regression of the zooid of Perophora into a stolon and the subsequent differentiation of a new zooid from this stolon.
2. Circulatory cells of the stolon resulting from regression will aggregate into masses larger than the minimal size necessary for differentiation of a zooid, but fail to differentiate into a zooid.
3. The cells of a zooid after staining with neutral red appear in the stolon during regression and finally come to lie in the newly formed zooid.
4. During the cycle of adult zooid to stolon to newly formed zooid, there is no evidence for cell division from studies with tritiated thymidine.
5. It is concluded that under conditions of starvation, an adult zooid furnishes all the cells for the formation of a stolon and the subsequent zooids without cell division.