28 Nature threatened 
the bottom of the sea like an enormous 
steam plough, and thus completes the 
destruction begun by the large sweep 
nets used nearer the surface. Thus 
there has arisen an imperative need 
for a rational regulation of the exploi- 
tation of marine life. Indeed, this is 
felt to be quite as urgent a necessity 
as in the case of the magnificent 
mammals of Africa, the fur-bearing 
animals of Siberia and Canada, and 
the gaily coloured birds of the tropical 
forests. For, is it not true that an 
exterminated species of animal or 
plant is gone for ever ? 
The beaver {Castor fiber) formerly 
occurred over the whole of Europe 
except the extreme north. This is 
clear from fossil finds, and from names 
of rivers, lakes, and bogs. In Ger- 
many, for instance, I know more than 
300 localities whose names are derived 
from that of the beaver. In Sweden, 
