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Fourth. The Evidence of Mimicry. — Not infrequently 

 organisms are met witli in the animal and vegetable king- 

 doms which closely simulate the appearance, and sometimes 

 the habits, of other organisms. 



The chameleon, it is well known, by certain changes in 

 the pigment-cells of the skin, has the power of assimilating 

 its colour to that of its surroundings, which is a clear advan- 

 tage to any animal that, for any reason, may desire to lie 

 perdu. The stripes of the tiger simulate the coarse colour- 

 ing of tropical grass ; the skin of the lion is tawny — 

 the colour of his habitat, the desert sand. In some degree 

 mimicry is the reason why a keen eye discovers so little 

 evidence of life in the open, which we know is full of life. 

 There are butterflies which closely resemble leaves and 

 bits of stick. One has to look intently to distinguish the 

 larger snakes from the branches round which they wind 

 themselves, as one may see any day at the Zoological 

 Gardens ; where also there is a green toad, not easily 

 discoverable amid the foliage of his abode. Hen-birds that 

 sit in open nests are dull and unattractive of hue. Spiders 

 associating with ants become antlike in form and colour. 

 Bates, in his travels, speaks of having been considerably 

 frightened by a species of huge caterpillar, which had 

 assumed the appearance of a poisonous snake. The only 

 explanation sufficient to account for these facts is, that any 

 little modification tending to make one species more like 

 another, where such likeness is an advantage either for 

 protection or attack, will tend to be preserved ; and gradu- 

 ally such favouring peculiarities of resemblance will become 

 closer and more numerous. Thus the fact of mimicry is 

 not merely explained by the theory of natui-al selection, 

 but affords an important argument in support of that theory. 



Fifth. Classification. — All naturalists have tried to 

 arrange living creatures according to their essential and 

 structural affinities. ' ' Community of descent,'' says Darwin, 

 " was the hidden bond which they had been unconsciously 

 seeking." Now, of forms still living, the various kinds often 

 approach each other so nearly, and at so many different 

 points, that no two naturalists will precisely agree as to a 

 system of classification. To take a glaring instance. The 

 differences between animals and plants would appear to be 

 sufficiently characteristic. There is no difficidty in distin- 

 guishing organisms so dissimilar as Oscar Wilde and his lily. 

 But, in the lower series, the animal and vegetal characters 



