SPECKLED TROUT. 117 



in broader waters, where large food is far 

 more abundant, but where shoals of small 

 fish would starve. The peculiarities thus 

 impressed upon them have been handed 

 down to their descendants, till at length 

 they have become sufficiently marked to 

 justify us in regarding them as a separate 

 species. But it is difficult to say what makes 

 a species in animals so very variable as fish. 

 There are, in fact, no less than twelve kinds 

 of trout wholly peculiar to the British Islands, 

 and some of these are found in very restricted 

 areas. Thus, the Loch Stennis trout inhabits 

 only the tarns of Orkney ; the Galway sea 

 trout lives nowhere but along the west coast 

 of Ireland ; the gillaroo never strays out of 

 the Irish loughs ; the Killin charr is confined 

 to a single sheet of water in Mayo ; and other 

 species belong exclusively to the Llanberis 

 lakes, to Lough Melvin, or to a few mountain 

 pools of Wales and Scotland. So great is 

 the variety that may be produced by small 

 changes of food and habitat. Even the 



