2 9 o ANIMAL DEFENCES 



In summer it is of a bright reddish -brown colour, with the ex- 

 ception of the under parts, which are yellowish -white, and the 

 end of the tail, which is black. But in winter the entire coat, 

 save only the tip of the tail, becomes white, and in that condition 

 the animal is known as an Ermine. A similar example is afforded 

 by the Weasel (Mustela. vulgaris\ The seasonal change in the 

 vegetarian Irish Hare is purely of protective character, but in such 

 an actively carnivorous creature as a Stoat or Weasel it is aggres- 

 sive as well, rendering the animal inconspicuous to its prey. 



Among Birds no better example can be selected than the 

 Ptarmigan (Lagopus mutus) (fig. 479), native to the Scottish 



Fig. 479. Ptarmigan (Lagopus mutus), in winter plumage 



Highlands among other places. The summer plumage of this 

 bird is brown with darker markings, but in winter it is pure white, 

 except that the outer tail-feathers remain black, and the male bird 

 retains a black band in front of the eye. 



COLOUR-CHANGE IN CHAMELEONS. The power of adjusting its 

 colour to suit the surroundings in the Chameleon is almost pro- 

 verbial, and the change here takes place with extreme rapidity. 

 As in the Stoat, it is quite as much aggressive as protective in 

 nature. The colour -change in this case is brought about by 

 alterations in the size of pigment -holding cells contained in the 

 deeper part of the skin. Under the influence of the nervous 

 system these can either be contracted to mere spots, or relaxed 

 into branching star-like forms. Since they are arranged in a 

 number of layers and contain different sorts of pigment, it is 



