136 ASSOCIATION OF ORGANISMS—THE WEB OF LIFE 
but has been hunted down to such a deplorable extent, chiefly for 
the sake of its fur, that it now exists in greatly diminished num- 
bers, and in all probability will become extinct at no distant 
period, except in cases where it is strictly preserved. It was 
once a native of Great Britain, though its range never extended 
to Ireland. According to Geraldus Cambrensis it lived in the 
river Teifi (Cardiganshire) so late as 1188, and is thought to 
have survived in Scotland to a still later period. The American 
Beaver is probably a distinct species (C. Canadensis), and its 
habits have been more carefully studied than those of the Euro- 
pean kind. The animal is an expert swimmer and diver, being 
modified in structure in connection with this habit, as elsewhere 
described (see vol. iii, p. 73). In all probability it was originally 
a bank-dweller, excavating an upwardly sloping burrow, with 
the top end expanded into a living chamber, and the entrance 
below the surface of the water. And where this unfortunate 
animal is subjected to much persecution its architectural efforts 
do not attain anything of more elaborate nature. Under normal 
circumstances, however, much more complex homes are made, 
which may be regarded as having been evolved by gradual 
stages from the primeval burrow. They involve the construction 
of “dams” and “lodges”, a narrow stream being converted by 
the former into a series of ponds, of which the surface-level re- 
mains fairly steady, thus giving favourable conditions for building 
the lodges or houses. It is essential that the district should be 
well wooded, as the chief material used in making the dams con- 
sists of the trunks and branches of trees, some of which may be 
as much as 40 inches round at the base and 120 feet high. The 
tools employed are the powerful incisor teeth, and a tree is felled 
by being bitten round in a neat manner near the ground. As 
H. T. Martin says (in Castorologza):—‘ No better work could 
be accomplished by a most highly-finished steel cutting tool, 
wielded by a muscular human arm”. 
Trees growing near water usually slant towards it, and when 
sufficiently weakened by the gnawing process must, as a rule, fall 
that way. It was once supposed that the Beaver secured this 
end by biting more wood from the side facing the stream, but 
this appears to be incorrect. When the tree is felled its branches 
are gnawed off, and the timber is cut up into lengths of five or 
six feet, the bark being peeled off to serve as food. It is, indeed, 
bid 
