140 ASSOCIATION OF ORGANISMS—THE WEB OF LIFE 
of those who visit beaver-districts, and yet no greater disappoint- 
ment awaits the inquirer than the first inspection of one. Some- 
how the minds of all lovers of natural history become affected by 
the fabulous accounts concerning this structure, and it is a shock 
to stand for the first time before a pile of twigs, branches, and 
logs, heaped in disorder upon a small dome of mud, and to learn 
that this constitutes the famous lodge. Of course the superficial 
glance does not convey all that can be learnt in connection with 
this work, but it does most completely disillusionize the mind. 
On breaking through the upper walls, the interior is found to be 
similar to the general type of an animal’s sleeping apartment, and 
has scarcely any distinguishing characteristic. . . . Starting with 
the simple burrow, the next step is the accumulation of logs and 
branches about its entrance, forming what is called a ‘bank-lodge’. 
In places where the water is shallow towards the shore, a great 
advantage would be derived from extending this artificial cover- 
ing of brushwood, so that in time a natural evolution of the lodge 
disconnected entirely from the shore would take place, and form an 
independent and very convenient refuge from landward enemies.” 
It may be well to add that the large flattened tail of the beaver 
is a swimming organ, and is not employed as a trowel. Clay is 
manipulated entirely by means of the fore-paws. 
Recognition Marks and Odours.—Many of the gregarious 
Mammals possess contrasted light and dark markings which pos- 
sibly enable the individuals of the same species to recognize one 
another, as in the similar cases already described for birds (p. 132). 
The most familiar instance is the white patch on the under side 
of a Rabbit’s tail, which, though it does not interfere with the 
general protective character of the coloration, makes the animal 
easily seen when it moves rapidly. On this account it has also 
been described as an illustration of ‘signalling coloration”, by 
which, when retreating from danger, an unconscious warning is 
given by the animal to its fellows. Other instances cited by 
Wallace (in Darwinzsm) are antelopes (fig. 1106), zebras, mon- 
keys, and lemurs. In regard to the first of these, he suggests 
that the great variety in the shape of the horns has to do with 
recognition. 
Gregarious Mammals are commonly distinguished by the 
possession of a keen sense of smell, which has various relations 
to habits. In herbivorous forms, for instance, it is of great 
