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Quarterly Journal of Microscopical Science, Vol s3-103, 531-541, Copyright © 1962 by Company of Biologists

Naked Axons and Symmetrical Synapses in Coelenterates

G. A. HORRIDGE 1 and BRUCE MACKAY 2

1 Gatty Marine Laboratory and Department of Natural History, St. Andrews, and the Department of Anatomy, Edinburgh
2 Gatty Marine Laboratory and Department of Natural History, St. Andrews, and the Department of Anatomy, Edinburgh; Present address is Department of Anatomy, State University of Iowa, Iowa, U.S.A.

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 (= {gamma}-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.






© The Company of Biologists Ltd 1962