36 



THE SEA-TROUT 



Loch Lomond trout, there having been an uninterrupted coming and 

 o-oino- for centuries from and to the sea, the stock has retained 

 all the marked outward characteristics of the migratory fish. But so 

 far as structure and outline are concerned the isolated trout from above 

 the Falls of Clyde differ in no respect that I can discover from the 

 trout or sea-trout below the Falls. 



It may of course be objected that the strain of each distinct species 

 in the loch (assuming for the sake of argument that the migratory and 

 non-migratory fish are distinct species) has been affected by inter- 

 breedino- over Ions; aees, and that each has in consequence approached 

 closely in its general characteristics to the other without wholly losing 

 its proper individuality. But as to this matter of the crossing of breeds, 

 in his great work " On the Origin of Species," Darwin makes this 

 pregnant observation : — " The possibility of making distinct races by 

 crossing has been greatly exaggerated .... Certainly, a breed inter- 

 mediate between Izvo very dhtinci breeds could not be got without 

 extreme care and long-continued selection ; nor can I find a single case 

 on record of a permanent race having been thus formed." He also 

 states : — " It is difficult, perhaps impossible, to bring forward one case 

 of the hybrid offspring of two animals clearly dhlhict being themselves 

 perfectly fertile." We all know, moreover, his views as to the origin 

 of our various breeds of pigeon : — "Great as the differences are between 

 the breeds of pigeons, I am fully convinced that the common opinion 

 of naturalists is correct, namely, that all have descended from the rock- 

 pigeon {Colitmha livid)'' a passage which it is interesting to contrast 

 with another written two hundred vcars earlier, to this effect : — "And you 

 are to note, that there are several kinds of trouts : but these several 

 kinds are not considered but bv very few men ; for thev go under the 

 general name of trouts : just as pigeons do, in most places." The 

 reader may be referred, for the rest of the passage, to Izaak Walton, 

 his book. On the whole, it would seem to be more in accordance with 



