8 



SALMONIDiB 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 diflferenoe not being permanent merely 

 resolves itself into a local race or inconstant variety. The number of vertebrte 

 and the cascal appendages have been considered as characters which may 

 materially assist in fixing the locality of a species among the Salmotiida; and it is 

 proposed investigating in detail some of the various structural and functional 

 differences that have been brought forward for the purpose of establishing species 

 among the true salmon, Salmoncs. It has occuri'cd that owing to too great 

 importance having been given to inconstant variations the number of species 

 among this family has been unduly augmented, and varieties have been accorded 

 specific rank : while every little variety of form, colom-, 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, insufficiency of food, or 

 sickno.ss from any cause. The head of the male is generally longer than that of 

 the female, especially in old examples, but these firoportions 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 tlie colours 

 are not very far removed from those of the local brook trout : and other as remarkable deviations 

 from the original type will be alluded to when this local race is described. 



ST.VKE Olt KETTLH NET, 



