The Origin of the Markings of Caterpillars. 283 



thus have a case of the acceleration by natural se- 

 lection, of processes determined by innate causes. 

 Why changes should predominate in the last 

 stage, is a question closely connected with that of 

 the causes of larval markings in general, and may 

 therefore be investigated later. 



But if we here assume in anticipation that all 

 new markings depend on adaptation to the con- 

 ditions of life, and arise through natural selection, 

 it will not be difficult to draw the conclusion that 

 such new characters must prevail in the last stage. 

 There are two conditions favouring this view; 

 the size of the insect, and the longer duration of 

 the last stage. As long as the caterpillar is so 

 small as to be entirely covered by a leaf, it only 

 requires a good adaptation in colour in order to be 

 completely hidden ; independently of which, it is 

 also possible that many of its foes do not consider 

 it worth attacking at this stage. The last stage, 

 moreover, is of considerably longer duration than 

 any of the four preceding ones ; in Deilephila 

 Euphorbia this stage lasts for ten days, whilst 

 the remaining stages have a duration of four days ; 

 in Sphinx Ligustri the last stage also extends 

 over ten days, and the others over six days. 



In its last stage, therefore, a caterpillar is for 

 a longer period exposed to the danger of being 

 discovered by its foes ; and since, at the same 

 time, its enemies become more numerous, and its 

 increased size makes it more easy of detection, it 



