Tissue dynamics of steady state growth in hydra littoralis. III. Behavior of specific cell types during tissue movements

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Abstract
Hydra tissues continuously move from the growing column to the body extremities. To study the cellular basis of these movements, mosaic hydra were produced by grafting portions of isotopically labeled animals to portions of unlabeled ones. The progressions of labeled cells away from the original graft site were determined by the method of radioautography. From the data obtained, it is possible to deduce the migratory relations between different cell types and the patterns of their movement.Most cells move in the form of coherent expanding epithelia, in which cells do not individually wander relative to neighboring cells. The gastrodermal tissue sheet includes the gland and digestive cells; the epidermal tissue sheet includes the interstitial and epitheliomuscular cells. These tissues move distally and proximally from a “stationary region,” near the top of column. The two epithelia do not move at the same rate, however, and their stationary regions are at different column levels.Nematocytes migrate in an amoeboid fashion from the body column to the tentacles. They migrate along the epidermal muscular layer, and do not move through the mesolamella to the gastrodermis. These aspects of cell behavior are consistent with the histological structure of hydra.
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