DISPERSION OF FRESH-WATER FISHES. 1 19 



that at some time spawn or even young fishes may 

 have been carried across by birds or other animals, 

 or by man, or more likely by the dash of some 

 summer whirlwind. Once carried across in favor- 

 able circumstances, the species might survive and 

 spread. 



I saw last summer an example of how such 

 transfer of species may be accomplished, which 

 shows that we need not be left to draw on the 

 imagination to invent possible means of transit. 



There are few water-sheds in the world better 

 defined than the mountain range which forms the 

 " backbone " of Norway. I lately climbed a peak 

 in this range, the Suletind. From its summit I 

 could look down into the valleys of the Lara and 

 the Bagna, flowing in opposite directions to oppo- 

 site sides of the peninsula. To the north of the 

 Suletind is a large double lake called the Sletnin- 

 genvand. The maps show this lake to be one of 

 the chief sources of the westward-flowing river 

 Lara. This lake is in August swollen by the 

 melting of the snows, and at the time of my visit 

 it was visibly the source of both these rivers. 

 From its southeastern side flowed a large brook 

 into the valley of the Bagna, and from its south- 

 western corner, equally distinctly, came the waters 

 which fed the Lara. This lake, like similar moun- 

 tain ponds in all northern countries, abounds in 

 trout; and these trout certainly have for part of 

 the year an uninterrupted line of water communi- 

 cation from the Sognefjord on the west of Norway 

 to the Christianiafjord on the southeast, from the 

 North Sea to the Baltic. Part of the year the lake 



