The Reorganization of Tissue Masses ofCordylophora Lacustrisand the Effect of Oral Cone Grafts, with Supplementary Observations onObelia Gelatinosa

Abstract

ABSTRACTA method is described for the preparation of reconstitution masses from the expressed coenosarc tissues of Cordylophora lacustris. This brackish water hydroid is more suitable for the purpose than others which have so far been used. Under normal conditions (50 % sea water at 16–17° C.) such masses produce one or more hydranths within about 2 days and often additional unorganized outgrowths. The main histological features of the reconstitution masses as seen in sections are described. From these observations and from experiments with masses made from isolated ectoderm and endoderm it is concluded that there is no reduction of the cells to a pleuripotent condition. The cells of each original layer can form only the layer from which they were derived. Masses made from endoderm cells only are incapable of holding together for long and soon disintegrate. Pure ectoderm masses, however, rapidly round up and form hollow vesicles but do not produce hydranths. No signs of cell division during reconstitution were detected. The “interstitial” cells observed in the coenosarc ectoderm are thus not able to differentiate into endoderm when this is absent and there is no indication that they perform any essential part in the process of reconstitution. An oral cone when grafted into a mass will determine the position of the regenerated Hydranth which develops in relation to the graft. Evidence is given to prove that the action of the cone is one of pure induction and that it does not supply cells to the induced hydranth. The action of the cone is independent of its orientation and it will produce its effect even after previous chopping up and reuniting. Attempts to graft killed oral cones have so far failed. Grafts of distal halves of young gonophores do not induce hydranths. Calcium or magnesium deficiency in the medium results in complete suppression of hydranth formation from masses but not always of unorganized outgrowths. Oral cone grafts, however, can overcome this inhibition and tentacles are formed. A similar inhibitory effect is produced by potassium deficiency, but is not overcome by an oral cone graft. The quantity of calcium required to permit tentacle formation in plain masses is very small (c. 0·00006 M). Sodium cyanide (c. M/30,000), phenyl urethane (c. M/3000) and low temperature (5·5–0·5° C.) can inhibit hydranth formation in plain masses, but oral cone grafts overcome this inhibition and induce the formation of tentacles. Reconstitution masses which produced hydranths were also made from the coenosarc of another brackish water hydroid Obelia gelatinosa. Isolated ectoderm and endoderm were incapable of reorganization. Mixed masses of Cordylophora and Obelia coenosarc separated into regions composed of tissue from one species only and each produced hydranths independently.