Inquiries into the philosophy of zoology / by R. Knox.

  • Robert Knox
Date:
[1855]
Catalogue details

Licence: Public Domain Mark

Credit: Inquiries into the philosophy of zoology / by R. Knox. 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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    these mesial teeth begin to fall out and' are not replaced, the teeth on the chevron remaining to tlie last. In the sea trout, as in the sal- mon, the progress of edentulation is from behind forwards, and the process goes on until they are not unfrequently reduced* to two or three, at which point, in respect of its dentition, the true salmon and .the Fario are identical, or nearly so. Thus the dentar formula of the French naturalist is again at fault. By it alone, the true salmon, from the smolt upwards to the fish of 2 lbs. weight could be distinguished neither from the common trout nor sea trout or forelle; and now we find, that by it alone, the full-grown forelle can scarcely, if at all, be distinguished from the true salmon.. III. Let us now apply the formula to the fish called the Salmo Trutta or common trout, lacustrine, and riverine. In the young of all species the dentition is the same. The vomer carries the two kinds of teeth, the transverse and the longitudinal, perfectly distinct. The posterior are arranged in a double interrupted or undulating row, and extend well back on the body of the vomer; the group of teeth in front, already spoken of as the transverse teeth or those of the chevron, are well marked, and quite identical with the species of all the genera of the Salmonidse. In certain large lacustrine trout I have examined, weighing from 6 to 12, and in one of 20 lbs, there was a double row of teeth on the body of the vomer, but the anterior group on the chevron had disappeared. Thus the law of edentulation in these lacustrine trout was the reverse of that subsisting in the true salmon and Fario, but I do not mean this to be applied to all the species of lacustrine trout, for I have not examined all; and the longer I live and the more extended my inquiries are, the more deeply am I con- vinced of the error of applying natural-history views derived from the examination of species and genera of one continent or of one country to those of another. Nature admits not of the restrictions laid down by naturalists; an European fact is not an African or Asiatic one,—still less is it kosmic. As to the river trout I have examined, from a few ounces to 10 or 12 lbs. weight, I have found the law of their dentition to be a double row of teeth upon the body of the vomer, and, in addition, a group of transverse teeth on the fore part of the same bone, perfectly distinct. That there may be riverine species which lose the anterior group, and others which retain these but lose the posterior or mesial, 1 will neither affirm nor deny; I speak only of what I have seen. For rea- sons to be afterwards stated, I am inclined to think that this will be found to be the case. XIIT. 2 K
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