Horridge, George AdrianMackay, Bruce2019-09-090370-2952http://hdl.handle.net/1885/165914Summary Examination of sections of the marginal ganglion of the jellyfish Cyanea and the hydromedusan Phialidium by the electron microscope, in a region where nervous tissue is readily identified on account of its abundance, reveals the following features. Nerve-cell bodies and axons are crowded together without special glial cells. The axons form a layer between the cell-bodies and the mesogloea and the spaces between them are continuous with other intercellular spaces and with the mesogloea. Features typical of nerve-cells in other animals are mitochondria, Golgi region (= γ-cytomembranes), neurotubules (= canaliculi) about 16 mµ wide, and several types of vesicle ranging in size from 50 to 200 mµ, including synaptic vesicles of 50 to 100 mµ. Features not typical of nerve-cells are the modified (possibly sensory) cilia on the dendrites of bipolar cells and the absence of clumps of Nissl substance and neurofilaments. Synapses between axons (or with a perikaryon) have a synaptic cleft of 18 to 22 mµ and a crowded row of synaptic vesicles within the neurones on each side of the synapse.17 pagesapplication/pdfen-AU© 1962 by the Company of Biologists LtdjellyfishCyaneahydromedusanPhialidiumaxoncoelenterateganglion1962-12-0110.1038/204499b0