j6 BRITISH FRESHWATER FISHES 



epoch, migratory Char were to be found much 

 farther south than at the present day, and that 

 these descended to the sea in spring, and towards 

 the winter re-entered the rivers to spawn, as they 

 do now in the Arctic regions. Our Char, therefore, 

 represent a number of lacustrine colonies of one or 

 a few migratory ancestral forms, to which they 

 stand in much the same relation as our river and 

 lake Trout do to the Sea-trout, with the important 

 exception that they are isolated, and have been so 

 since the end of the glacial epoch, perhaps nearly 

 100,000 years. 



The word " isolated " is here used to mean that 

 the migratory Char retreated northward, and the 

 lacustrine colonies were thus cut off from any 

 chance of reinforcements from the sea ; the complete 

 isolation of the Char in any particular lake or 

 system of lakes from those of neighbouring lakes or 

 lake systems may have taken place either long ago 

 or quite recently, according to local geological 

 changes. 



At the present day our lake and river Trout are 

 continually reinforced from the ranks of the Sea- 

 trout, and when they are found in localities now 

 inaccessible to the latter there does not seem to 

 have been any long-standing isolation ; consequently 

 there are in our islands no races or incipient species 

 of Trout which are recognizable and definable. 



The case is quite otherwise with the Char, which 

 I have studied with particular attention for some 

 years. The Char of the Lake District {Salvelhius 

 willughbii) and its close ally, 5. colii^ from the 

 west of Ireland, probably come nearest to the 

 migratory ancestral form. In several of the Scottish 



