Studies on Hydroid Differentiation, II. Colony Growth and the Initiation of Sexuality

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Abstract
The colonial hydroid, Podocoryne carnea, is admirably suited to the study of differentiation (Braverman, 1962a). A colony growing on the shell of the marine snail Nassa consists of nutritive and generative zooids rising from a highly ramified and anastomosing stolon. If, instead of a snail, the shell is occupied by a hermit crab, a third type of person, the spiralzooid, is found on the dorsal lip of the shell (Cazaux, 1958; Braverman, 1960). Good descriptions of the animal appear in Allman (1871) and Berrill (1953). A single nutritive zooid removed from a colony and placed on a microscope slide in standing sea water attaches to the slide and gives rise to a colony. Colony growth consists of the formation of stolons attached to the substrate and of the appearance of zooids—first nutritive, then generative—on the stolons.