TUBULARIA REGENERATION: RADIAL ORGANIZATION OF TENTACLES, GONOPHORES, AND ENDODERM

¹ Station Biologique, Arcachon, France
² Department of Organismic Biology, University of California, Irvine, California 92664

1. The stalk of Tubularia is divided by several cellular septa. There is a gradient in cell height from septal to interseptal planes. Septal cells can thus be interpreted as manifestations of a single (repeating) developmental or histological gradient, rather than as unique cells in an otherwise homogeneous epithelium.

2. When a hydranth regenerates from a segment of Tubularia stalk, the tentacles, gonophores and hypostomal ridges (taeniolae) arise in relation to this pre-existing radial organization of the stalk.

3. Tentacles appear in such positions that endodermal septal planes are intertentacular. Gonophores form in pairs, one on each side of every septal plane, between the first and second tentacle. Taeniolae arise along the septal, and later along other intertentacular planes.

4. These and other relations suggest that the visible radial order of the hydroid polyp is a manifestation of a fundamental, domain-like radial tissue organization.