. British and Irish Salmonidæ. Salmonidae. 8 SALMONID^ OF BRITAIN. certain local varieties or races. If, however, the variations are not of a persistent character, nor exceed the differences between the limits laid down for a species, these cannot be considered as indicating a distinct species :_ for to render such valid, we must have a permanence of variation from the original form. Thus, among the sticklebacks we find in the ten-spined form, some possessing ventral fins, others destitute of them ; but this diflference not being permanent merely resolves itself into a local race or inconstan
. British and Irish Salmonidæ. Salmonidae. 8 SALMONID^ OF BRITAIN. certain local varieties or races. If, however, the variations are not of a persistent character, nor exceed the differences between the limits laid down for a species, these cannot be considered as indicating a distinct species :_ for to render such valid, we must have a permanence of variation from the original form. Thus, among the sticklebacks we find in the ten-spined form, some possessing ventral fins, others destitute of them ; but this diflference not being permanent merely resolves itself into a local race or inconstant variety. The number of yertebrjB and the c£ecal appendages have been considered as characters which may materially assist in fixing the locality of a species among the Sahnonidoi, and it is proTDOsed investigating in detail some of the various structural and functional diiferences that have been brought forward for the purpose of establishing species among the true salmon, Salmones. It has occurred that owing to too great importance having been given to inconstant variations the number of species amono- this family has been unduly augmented, and varieties have been accorded specific rank : while every little variety of form, coloui', or structure has also been reckoned as possibly demonstrating hybridity. The proportions of different parts of the body vary with age, season, or locality,* and this may be augmented in some anadromous forms which have been subjected to unnatural retention in fresh water, insufiiciency of food, or sickness from any cause. The head of the male is generally longer than that of the female, especially in old examples, but these proportions are liable to variation should the example be barren. * Young Lochleven trout, raised by Mr. Andrews of Guildford, from eggs sent from Howietoun, are found to grow more rapidly in their southern home, become deeper in form, while the colours are not very far removed from those of the local brook trout: and other
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectsalmoni, bookyear1887
