150 NATURE'S TEACHINGS. 



leaf, the resemblance extending not only to the form, but the 

 colour. All entomologists are familiar with many similar 

 examples in insect life. The common Tortoise-shell Butterfly, 

 for example, has a way of settling on patches of red soil, with 

 which it harmonizes so well that it can hardly be seen. The 

 various moths, also, are in the habit of resting on tree-bark, 

 palings, and other objects, to which they instinctively know 

 that they assimilate in hue. Many a beginner in entomology 

 will pass a wooden fence or a wall, and not see an insect on 

 either, while an adept will follow him and take twenty or 

 thirty good specimens. 



The last figure in the illustration represents a Ptarmigan 

 (Lagopus vulgaris) in its winter dress. These birds have two 

 differently coloured dresses, one for summer and the other for 

 winter, and both adapted for concealment by imitation. In 

 the former dress it is mottled with various shades of blackish 

 brown, yellow, and white. As the bird is in the habit of 

 settling among the grey lichen-covered stones on the sides of 

 rocky hills, these colours harmonize so exactly with them that 

 a Ptarmigan may almost be trodden upon before it is perceived. 



In the winter, when the snow covers the whole country with 

 one uniform sheet of white, except where the wind blows the 

 snow aside, and exposes the underlying stones, the Ptarmigan 

 assumes a different plumage, being almost entirely white, 

 except a black streak over the eye, and the outer feathers of 

 the tail, which are also black. Thus the bird becomes almost 

 indistinguishable from a snow-covered stone, especially as it has 

 a habit of squatting motionless and silent when it takes alarm. 



The reader may, perhaps, remember that the common Stoat 

 also has a summer and winter dress. The ordinary colour is 

 rich reddish brown above, and white beneath, with a black tip 

 to the tail. In the severe winters of Northern Europe the 

 Stoat exchanges his ruddy coat for one of pure white, and is 

 then known by the name of Ermine. It is remarkable that in 

 the winter dress both of the Ptarmigan and Stoat the tail is 

 black, while the rest of the coat is white. 



THE TRENCH. 



WE now come to a third mode of concealment in war, 

 namely, that which is obtained by means of Trenches or Pits. 



