244 THE INFANCY OF ANIMALS 



they are not essential to present-day conditions, are not 

 responses to present-day needs, is shown by the fact that 

 they have become eliminated in most of the " bony " 

 fishes of to-day. 



In other words, owing to the prolonged period of larval 

 life, caterpillars have been subjected to the action of 

 Natural Selection no less rigorously than in the case of 

 the adults. Hence it is that caterpillars display an amazing 

 variety of shape and coloration, and methods of defence ; 

 so great is the range of differences in these particulars that 

 it is impossible in these pages to do more than select one 

 or two of the more striking instances. 



Caterpillars being succulent morsels, and incapable of 

 offering active resistance to their enemies, have had to 

 resort to passive measures — coloration, unpalatability, 

 defensive armour, and the simulation of foreign objects. 

 One has only to turn over the pages of entomological 

 volumes which are furnished with coloured plates, to 

 discover at a glance how extraordinarily varied are the 

 hues of caterpillars. 



Many are " protectively " coloured : obviously agreeing 

 so closely with the prevailing hues of their surroundings 

 as to make detection a matter of extreme difficulty. 

 Such are the green-coloured individuals, or those in 

 which the ground colour is green, relieved by horizontal 

 or oblique stripes of white or pink, as in so many of the 

 caterpillars of the hawk-moths. Herein the green merges 

 with that of the leaves of the food-plant, while the stripes 

 more or less closely imitate the mid-ribs and narrow stems 

 of such leaves. This type of coloration renders detection 

 difficult even to keen-eyed birds. And it is found that 

 caterpillars so coloured are always greedily eaten when, 

 by chance, they are discovered. 



