Summary
A subectodermal nerve-net is demonstrated in ten species of Ctenophores by means of either Methylene Blue vital staining or silver impregnation. There is no evidence of subendodermal nerve-net. The ectodermal nerve-net displays a characteristic polygonal pattern which is thought to result from morphogenetic events. Both bipolar and tripolar neurones occur.
Three types of concentrations of nervous tissue are described: a) a high accumulation of nervous perikarya at the aboral sensory pole; b) a noticeable densification of the net along the eight meridional ciliary strands of every species, and around the lips of Beroidea; c) in the Cydippids Pleurobrachia and Hormiphora two thick strands of fibers and neurones interconnecting the aboral organ and the tentacles: the tentacular nerves.
Ultrastructural evidence is given for the presence of nervous elements under and amidst ectodermal epithelial cells. Three features allow the recognition and characterization of neurites and neurones: a) numerous clear and/or granulated vesicles; b) microtubules in variable amounts; c) frequent and highly differentiated synaptic contacts.
The very peculiar arrangement of the presynaptic elements is observed in all the species of Ctenophores so far studied. These synaptic contacts suggest chemical transmission in the nerve-net.
On the basis of ultrastructural evidence the author refutes the nervous nature previously attributed to the ciliated cells of the meridional grooves.
A parallel is drawn between nervous systems of Cnidaria and Ctenophora.
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Ce travail correspond à la première partie d'une thèse de Doctorat d'Etat, intitulée: «Système nerveux et intégration chez les Cténaires». Il a été effectué au sein de l'Equipe de Recherches Associée au C.N.R.S. no 183 (Directeur: Dr. Max Pavans de Ceccatty) et avec le concours du Centre de Microscopie Electronique Appliquée à la Biologie, de l'Université Claude Bernard.
Ce travail a bénéficié de la collaboration technique de Madame J. Amsellem que nous remercions vivement.
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Hernandez-Nicaise, ML. Le Système Nerveux des Cténaires. Z. Zellforsch 137, 223–250 (1973). https://doi.org/10.1007/BF00307432
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DOI: https://doi.org/10.1007/BF00307432