Fishes. 4781 



these mesial teeth begin to fall out and are not replaced, the teeth on 

 the chevron remaining to the last. In the sea trout, as in the sal- 

 mon, the progress of edentulatiou 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 riverioe. 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 3 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 1*2 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/ I 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. 



XIII. '2 K 



