Abstract
1. Histological structure of acontium of Diadumene luciae was studied by means of light-microscopical as well as electron-microscopical examinations. Certain indications were obtained that the whole surface of acontium was covered by a thin, continuous, uniformly ciliated sheet of protoplasm, which also separated the distal end of the cnidae from the exterior. It was very probable that the cnidae were situated in vacuole-like cavities among the epithelium, without any cytoplasmic coat such as to be called “cnidoblast”.
2. Peculiar refractile bodies of varying forms such as could be assumed as developmental stages of cnida were abundantly found in the acontia, which were in the course of regenerating either themselves or their cnidae. Evidence obtained from their study also pointed to the view that the cnidoblast had already been degenerated in the full-grown cnidae.
3. Remarks are given of some further findings as to structural elements of acontia and of cnidae, including the peculiar globular bodies, which were normally found within the acontia and were suggested as possible precursors of cnidae.
Most of the morphological findings included in the present note, as well as some of the points of view attained, may be summarized in diagram form as shown in Fig. 7.
