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 Darwinism) 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 



