Address to the physiological section / by W.H. Gaskell.

  • Gaskell, Walter Holbrook, 1847-1914.
Date:
[1896]
Catalogue details

Licence: Public Domain Mark

Credit: Address to the physiological section / by W.H. Gaskell. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    B. Coincidence of Structure and Physiological Function. 1. The simple non-glandular epithelium of the nerve tube coincides with the simple non-glandular epithelium of the alimentary canal, ciliated as it is in Daphnia.1 2. The structure and function of the cerebral hemispheres, olfactory lobes, and optic ganglia closely resemble the corresponding parts of the supra-cesophageal ganglia. 3. The structure of the right pineal eye, with its nerve end-cells and rhabdites, is of the same nature as that of a median arthropod eye. 4. The structure of the right ganglion habenulse is the same as that of the optic ganglion of the median eye. 5. The region of the hind brain, like the region of the infra-cesophageal ganglia, is concerned with the co-ordination of movements. 6. The region of the medulla oblongata, like the mesosomatic region of Limulus and its allies, is concerned especially with the movements of respiration. 7. The centres for the segmental cranial nerves resemble closely in their groups of motor cells and plexus substance the centres for the prosomatic and mesosomatic nerves, with their groups of motor cells and reticulated substance (Punkt-Substanz). 3. The third test is the ontogenetic test. The theory must be in harmony with, and be illustrated by, the embryonic development of the central nervous system. Such is the case, for we see that the nerve tube arises as a simple straight tube opening by the neurenteric canal into the anus, the anterior part of the tube, i.e. the cephalic stomach region, being remarkably dilated; the anterior opening of this tube, or anterior neuropore, is considered by most authors to have been situated in the infundibular region. Next comes the formation of the cerebral vesicles, indicating embryologically the constricting growth of nervous material outside the cephalic stomach. First, the formation of two cerebral vesicles by the growth of nervous material in the position of the ganglia habenulte, posterior commissure, and Meynert's bundle, i.e. the constricting influence of commissures between the optic part of the supra-ceso- phageal ganglia and the infra-cesophageal ganglia; then the formation of the third cerebral vesicle by the constricting influence of the IVth nerve and commencing cerebellum. Subsequently the first cerebral vesicle is divided into two parts by another nerve commissure—the anterior commissure, i.e. by nerve material joining the supra-cesophageal ganglia. Further, the embryological evidence shows that in the spinal cord region the nerve masses are at first most conspicuous ventrally and laterally to the original tube, such ventral masses being early connected together with the strands of the anterior commissure ; ultimately, by the growth of nervous material dorsalwards, the dorsal portion of the tube is compressed to form the posterior fissure and the substantia Rolaudi, the original large lumen of the old intestine being thus reduced to the small central canal of the adult nervous system. Finally, this nerve tube is formed at a remarkably early stage, just as ought to be the case if it represented an ancient alimentary canal. The ontogenetic test appears to fail in two points:— 1. That the nerve tube of vertebrates is an epiblastic tube, whereas if it repre- sented the old invertebrate gut it ought to be largely hypoblastic. 2. The nerve tube of vertebrates is formed from the dorsal surface of the embryo, while the central nervous system of arthropods is formed from the ventral surface. With respect to the first objection, it might be argued, with a good deal of plausibility, that the term hypoblast is used to denote that surface which is known by its later development to form the alimentary canal; thai in fact, as HeymcmV has pointed out, the theory of the germinal layers is not sufficiently well esta- blished to give it any phylogenetic value. It is, however, unnecessary to discuss Hardy and McDougall, Proa. C'amb. Philos. Soc. vol. viii. 1893. Heymons, Die Embryona.lcntmickl. v. Dermapteren it. Orthojtteren, Jena, 1895.