DISPERSION OF FRESH-WATER FISHES. 119 
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 
