202 Studies in the Theory of Descent. 



leaf, but generally near the end of a twig, where 

 young shoots are in close proximity. During 

 the embryonic development the eggs become 

 coloured, first yellow and partly blackish, and 

 finally completely black. 



First Stage. 



The young caterpillars (Fig. 37, PI. V.) 

 immediately after hatching measure four milli- 

 meters in length ; they are at first rather light, 

 but in the course of half-an-hour they are seen 

 by the naked eye to become of a deep velvety 

 black; later, on increasing in size, they again 

 become paler, appearing of a greenish-black, and 

 subsequently blackish-green. On further increas- 

 ing in size (Fig. 38), they are blackish-green, 

 with the horn, head, legs, and a crescent-shaped 

 chitinous plate on the back of the prothorax 

 black. There are also on the last segment a 

 double and two single black chitinous plates. Of 

 the later marking of the caterpillar there is 

 scarcely anything present. The spiracles appear 

 as white spots, and on each segment there are a 

 number (mostly ten) of small warts, each of which 

 emits a single bristle. 



When the young larvae have attained a length 

 of seven millimeters they are olive-green, and do 

 not contrast so brilliantly with the green of the 

 Euphorbia leaves as before ; neither do they as yet 

 possess any markings. 



