The Pleated Surface of the Undischarged Thread of A Nematocyst and Its Simulation by Models

The complex appearance in electron micrographs of sections, both transverse and longitudinal, of the undischarged thread of a nematocyst—the large holotrichous isorhiza of Corynactis viridis Allman—is compatible with the pleating of a tubular thread to form a triple-screw surface (Skaer & Picken, 1965). This interpretation of the sections was facilitated by a study of the properties of folded paper models, and by the construction of a three-dimensional wax model following, essentially, the method of His (1887), but with the difference that sections modelled in wax were serial electron micrographs of ultrathin transverse sections (Picken & Skaer, 1966). This wax model being fragile and opaque, it was subsequently cast in more robust and translucent Araldite resin by a cire perdu method.