The Origin of the Markings of Caterpillars. 247 



marking, the colour only becoming somewhat 

 darker. Length, twelve millimeters. 



Fourth Stage. 



The third moult (after another four days) like- 

 wise brings only a change of colouring, which is of 

 such a nature that the caterpillar becomes dimor- 

 phic. At the same time that peculiar roughening 

 of the skin takes place which, in the case of Chcero- 

 campa, was designated as " shagreening.'' The 

 colour is now light grass-green in some specimens, 

 and dark green in others ; in these last the sub- 

 dorsal line is edged above with dark brown, and 

 the spiracles are also of this colour. Length, 

 seventeen millimeters. 



Fifth Stage. 



Four days later, after the fourth ecdysis, the 

 dimorphism becomes a polymorphism. Five chief 

 types can be distinguished : 



Variety I. Light green (Fig. 7, PI. III.); dorsal 

 line, blackish-green, strongly marked ; subdorsal 

 line broad, pure white, edged above with dark 

 green ; spiracular line, chrome-yellow ; horn, 

 black, with yellow tip and blue sides. Spiracles, 

 blackish-brown, with narrow yellow border ; legs, 

 and extremities of prolegs, vermilion-red. 



Variety //.Blackish-brown (Fig. 6, PI. III.) ; 

 head and prothorax, yellowish-brown ; markings 

 the same as above. 



