Histological and ultrastructural study of the muscular and nervous systems in <i>Hydra</i>. I. The muscular system and the mesoglea

Abstract

Abstract The myonemes of the epithelio‐muscular cells of Hydra viridis were studied with the electron microscope. The myonemes are formed from fibers running parallel to the long axis of the polyp. The myoneme is a mixture of thick (200 Å diameter) filaments and thin (60 Å diameter) filaments. There was no indication of regular organization or spacing of the filaments. The filaments were attached to the membranes of the epithelio‐muscular cells at their ends. In these regions there were junctions between adjacent cells similar to the intercalated discs of vertebrate cardiac muscle. The possible role of these junctions in the transmission of an impulse along the length of the body column is discussed. The mesoglea consists of organized fibers dispersed in an amorphous ground substance. The pattern of organization of the fibers of the mesoglea is possibly a spiral and may be responsible for some of the morphogenic phenomena in Hydra which follow a spiral pattern.