Histological structure of epithelial hydra and evidence for the complete absence of interstitial and nerve cells

Abstract

Abstract Hydra were treated with colchicine, resulting in the elimination of interstitial, nerve, and stinging cells. These animals were cloned for several months and then examined histologically to determine: (1) the extent of cell depletion, and (2) the effect of this depletion on tissue structure and epithelial cell morphology. Thirteen of these hydra were serially sectioned for light microscopy and every cell was identified. All of the animals were composed solely of epithelial cells. No cells of the interstitial cell lineage, which includes interstitial cells, nerve cells, nematoblasts, and gametes, were found. Using experimental hydra with low numbers of interstitial and nerve cells, we verified that these cell types, when present, are readily identifiable in histological sections. Thus, we conclude that the cloned hydra are completely free of all cells except epithelial cells, and hence are defined as epithelial hydra . The histological organization of epithelial cells is normal in these animals. In each body region (hypostome, tentacles, gastricregion, peduncle, and basal disc) the organization of tissue and epithelial cell structure is normal. Therefore, epithelial cells are capable of autonomous region‐specific differentiations, and tissue architecture can arise independently of the interstitial cell lineage.