Formation of pattern in regenerating tissue pieces of Hydra attenuata. III. The shaping of the body column.

Excised pieces of hydra body tissue of varying size and shape regenerate into cylinders with a head and foot at opposite ends. The numbers of cells along the axial and circumferential dimensions were determined before, during, and after regeneration. The main process in shaping the excised tissue into a body column was found to be a rearrangement of the cells. When regenerates of different size were measured, the proportions of the body columns were found to vary, such that the smaller the animal the squatter the body column was. The presence of the head in regenerates was necessary for the formation or maintenance of the cylindrical shape, while the size of the head determined the proportions of the cylinder. The formation of a gradient of adhesivity induced by the developing head is suggested as the basis for the rearrangement of the cells into the cylindrical form.