Discussion of the origin of vertebrates : January 20 and February 3, 1910 / by Dr. W.H. Gaskell [and others].
- Linnean Society of London
- Date:
- 1910
Licence: In copyright
Credit: Discussion of the origin of vertebrates : January 20 and February 3, 1910 / by Dr. W.H. Gaskell [and others]. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![same position in the brain as the oesophagus in the Invertebrate group. Supra-infundibular nerve-mass was then the same as the supra-oesophageal, infra-infundibular as infra-oesophageal, and it was seen that the function corresponded marvellously. So powerful was the fetish of the inviolability of the alimentary canal, that no one of these observers ever noticed that if the infundibulum is the old oesophagus, it leads directly into the great cavity of the ventricles of the brain, which again lead into the straight narrow canal of the spinal cord and so through the neurenteric canal to the anus ; that in fact if the infundibulum is the oesophagus, the rest of the lining-walls of the cavity of the central nervous system corresponds word for word with the rest of the Invertebrate alimentary canal. On the contrary, they considered the homology could only hold good by turning the animal topsy-turvy and making the back of the Invertebrate correspond to the ventral surface of the Vertebrate. Such a method was doomed to failure and is now universally discredited. As to the alternative hypothesis of an origin from some non- .segmented Invertebrate, please think what it implies and consider seriously whether it is possible to accept it. I imagine we may take it for granted that we know the nature of all the main groups of animals alive on the earth at the present time, and as far as ] know the geological record has not brought to light any forms which are not capable of being classified either among or in con- nection with our present main groups; yet the assumption of this hypothesis is that from some unseginented animal low down in the scale a group of segmented animals has arisen, in which the alimentary canal was always ventral to the central nervous system and that this group gave origin to the Vertebrate. The absence of any evidence of such chain among living animals at all comparable to the well-marked evidence in the case of the Appendiculata, makes this hypothesis an improbable one; and when the hypo- thesis further necessitates that not only the central nervous s)'^stem of such segmented animals has been built up on exactly the same lines as the central nervous system of the Appendiculata, but, contrary to all other nervous systems, has been formed hollow, and that that hollow tube has been formed in such a shape and in such a position with respect to the true nervous elements as exactly to mimic the alimentary canal of the Appendiculata with respect to its central nervous system,—I ask you plainly, does not the improbability amount to an absurdity ? This I claim to be the great characteristic of the Vertebrate which differentiates it from all other animals—the presence and nature of this tube around which the central nervous system is grouped : and I beg that those speakers who follow after me and disagree with my conclusions, will give some explanation of the presence and peculiarities of this tube. To me and to all my friends who are accustomed to deal with the Vertebrate central nervous system, the explanation I have given is so self-evident and natural, that it is impossible to look at the matter in any other way.](https://iiif.wellcomecollection.org/image/b22427387_0008.jp2/full/800%2C/0/default.jpg)
