IX 



RECOGNITION-MARKS 171 



cabbage butterflies visited seven different orders, including 

 red, white, purple, yellow, or blue flowers ; the small tortoise- 

 shell visited an even greater range of flowers and colours, so 

 that we have no reason to impute to these insects anything 

 more than the power to recognise, after experience, any 

 conspicuous flowers that produce pleasant odours and, usually, 

 accessible honey. 



A consideration of the whole evidence as to the pur- 

 pose served by the excessively varied and brilliant colora- 

 tion of butterflies leads us to the conclusion that its 

 presence is due to general laws of colour-development — 

 some of which will be discussed in later chapters — whose 

 action is only checked when such development becomes 

 injurious. In the case of butterflies, the comparatively short 

 period that elapses between the emergence of the female 

 from the chrysalis and the deposition of her eggs, and the 

 still shorter period needed for the special functions of the 

 more brilliantly coloured male together with his power of 

 irregular but rapid flight, render it possible for the colour- 

 development to attain a degree of variety and beauty beyond 

 that of all other living things. The larvae of Lepidoptera 

 I in their countless myriads undoubtedly constitute an im- 

 portant factor in supporting the gloriously varied bird-life 

 of the tropics, as we have seen that they so largely support 

 that of our temperate zones. It is the comparatively small 

 surplus that escapes which is yet ample for the development 

 of the perfect insects in such abundance as to keep up an 

 I approximately equal supply of larvae for the next generation 

 ' of birds. When this is done they themselves become the 

 prey of birds, lizards, and other insect-eating animals. 



Some General Conclusions from Recognition- Marks 



We have thus been led by the study of colour as a means 

 of recognition by birds and mammals to some very important 

 general conclusions. The first is, that in both these groups, 

 it has primarily a still more important function, that of 

 facilitating the formation of new species during the early 

 stages of adaptation to changed conditions of life. Its 

 secondary, but still very important use in many groups, is for 

 easy identification as already described. That this is the 



