The Origin of the Markings of Caterpillars. 297 



become brown, but before this change they are 

 only to be found on green plants. 



Thus, it cannot well be doubted that the change 

 of colour is associated with a change in the habits 

 of life, and the question arises as to which has been 

 the primary change. 



If the view here entertained, that the later 

 brown coloration is adaptive, be correct, the species 

 must have first acquired the habit of concealing 

 itself by day on the ground and among dead 

 herbage, before the original green colour could 

 have been changed into brown by natural selec- 

 tion. This must represent the actual facts of the 

 case. 



Nearly allied species which at an advanced age 

 are not dimorphic, but are darkly coloured in all 

 individuals, are especially calculated to throw some 

 light on this point. For instance, the caterpillar 

 of Deilephila Vespertilio, which comes under this 

 denomination, is light green when young, and rests 

 both by day and night on the leaves of the plant 

 on which it feeds. As soon as it acquires its dark 

 colour after the third moult it changes its habits, 

 concealing itself by day on the ground and feeding 

 only by night. For this reason collectors prefer 

 seeking for it in the evening, or with a lantern by 

 night. 



The most instructive case, however, is that of 

 Deilephila Hippophaes, in which no change of 

 colour is associated with age, the caterpillar, 



