CHAPTER VIII 



PROTECTIVE RESEMBLANCE 



The colour of an organism is often due to the presence in 

 its semi-transparent tissues of substances which play a 

 part in some physiological process. Thus, leaf-green is 

 the colour of chlorophyll — the substance which enables 

 plants to build up living matter from the gases and salts 

 which they absorb from air and water. Similarly, the 

 aquatic larvae of certain midges (appropriately called 

 "blood worms") are red because their blood contains the 

 respiratory pigment haemoglobin, which takes up oxygen 

 from the air and transmits it to the tissues. Blood-red 

 and leaf-green may therefore be regarded as non-significant 

 in so far as the relation of the organ to its environment is 

 concerned. But many animals display a wealth of super- 

 added colour which has an important bearing upon the 

 life-history of the creature concerned. For instance, a 

 common use of colour is to assist an animal in escaping 

 from its enemies; and among insects we find numerous 

 examples of this kind. Protective resemblance, as it is 

 called, may be either general or special. In other words, 

 it may consist in a mere similarity of the insect's colouring 

 to its customary surroundings — to the background, so to 

 speak, against which it is commonly seen ; or the insect 

 may be an actual reproduction, in both colour and form, 

 of a definite object with which it is associated through- 

 out life. 



Instances of general protective resemblance are familiar 

 to all who have observed insects in their natural haunts. 



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