138 THE HAUNTS OF LIFE 



nearly the same in widely separated basins. 

 A lake in the Scottish Highlands, one of the 

 thousand lakes of Finland, a lake in Japan, 

 may have similar tenants. Why is this? It 

 is partly because water-birds carry the same 

 small animals on their feet, or in clodlets on 

 their feet, from one lakeside to another, because 

 the wind sometimes does the same, and because 

 changes in the surface-relief of the earth's crust 

 not only make valleys separate from one 

 another, but bring them together again. But 

 the most important reason is probably that the 

 animals which colonised the fresh waters came 

 for the most part from the shore, and that only 

 certain kinds of constitution could stand the 

 change. Let us think for a little what the 

 change from the shore to the fresh waters 

 would mean, always bearing in mind that it 

 would be a very slow and not a sudden change, 

 for most salt-water animals die immediately if 

 they are put into fresh water. 



FROM SALT WATER TO FRESH 



What characters or qualifications were 

 necessary before the transition from salt water 

 to fresh water could be even attempted ? 



