202 DARWINISM 



to Surinam (1810), had already exi)lained the matter. He 

 says : "The colour and even the shai)c of the hair are much 

 like withered moss, and serve to hide the animal in the trees, 

 but particularly when it has that orange-coloured spot l^etween 

 the shoulders and lies close to the tree ; it looks then exactly 

 like a piece of branch where the rest has been broken off, by 

 which the hunters are often deceived." Even such a huge 

 animal as the giraffe is said to be perfectly concealed by its 

 colour and form when standing among the dead and broken 

 trees that so often occur on the outskirts of the thickets where 

 it feeds. The large blotch-like spots on the skin and the 

 strange shape of the head and horns, like broken branches, so 

 tend to its concealment that even the keen-eyed natives have 

 been known to mistake trees for giraffes or giraffes for trees. 



Innumerable examples of this kind of protective colouring 

 occur among insects ; beetles mottled like the bark of trees or 

 resembling the sand or rock or moss on which they live, with 

 green caterpillars of the exact general tints of the foliage they 

 feed on ; but there are also many cases of detailed imitation of 

 particular objects by insects that must be briefly described.^ 



Protective Imitation of Particular Objects. 



The insects which present this kind of imitation most per- 

 fectly are the Phasmidne, or stick and leaf insects. The well- 



^ With reference to this general resemblance of insects to their environment 

 the following remarks by Mr. Poulton are very instructive. He says : 

 " Holding the larva of Sphinx ligustri in one hand and a twig of its food- 

 plant in the othei', the wonder we feel is, not at the resemblance but at the 

 difference ; we are surprised at the diihculty experienced in detecting so con- 

 spicuous an object. And yet the protection is very real, for tlie larvte will be 

 passed over by those who are not accustomed to their appearance, although the 

 searcher may be told of the presence of a large caterpillar. An experienced 

 entomologist may also fail to find the larvog till after a considerable search. 

 Tiiis is general protective resemblance, and it depends upon a general harmony 

 between tlie appearance of the organism and its whole environment. It is 

 impossible to understand the force of this protection for any larva, without 

 seeing it on its food-plant and in an entirely normal condition. The artistic 

 effect of green foliage is more complex than we often imagine ; numberless 

 modifications are Avrought by varied lights and shadows upon colours which are 

 in themselves far from uniform. In the larva of Papilio machaon the pro- 

 tection is very real when the larva is on the food-plant, and can hardly 

 lie appreciated at all when the two are apart." Numerous other examples are 

 given in the chapter on "Mimicry and other Protective Resemblances among 

 Animals," iu my Contiibutions to the Theory of Natural Selection. 



