8 



SALMONID^ OP BEITAIN. 



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 w-e find in the ten-spined form, some possessing ventral 

 fins others destitute of them; but this difference not being permanent merely 

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

 and the caecal appendages have been considered as characters which may 

 materially assist m fixing the locaHty of a species among the Salmonidm, and it is 

 proposed inve.stigating m detail some of the various structural and functional 

 differences 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 

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

 specific rank : while every little variety of form, colour, or structure has also 

 been reckoned as possibly demonstrating hybridity 



lnnJJ'%^'^?.°'f*^-''' °* l^^^^''* P*"*' °^ *^^ ^°^J ^^^y ^^^ age, season, or 

 locality,* and^this may be augmented in some anadxomous forms which have 

 been subjected to unnatural retention in fresh water, insufficiency of food or 

 ti?fpT«f°°'^"^iT^?'- , The head of the male is generally longer than that of 



SIAIiE OB KETTLE NET. 



