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 1 20 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 Castor ologia): "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, 



