178 Studies in the Theory of Descent. 



embryo the eggs first became yellowish-green, and 

 finally yellowish. 



First Stage. 



The young caterpillars are four millimeters in 

 length, and immediately after hatching are not 

 green, but of a yellowish-white opalescent colour, 

 the large and somewhat curved caudal horn being 

 black. The caterpillars were so transparent that 

 under a low magnifying power the nervous, 

 tracheal, and alimentary systems could be beauti- 

 fully seen. As soon as the larvae began to feed 

 (on Epilobium parviflorum) they became green in 

 consequence of the food appearing through the 

 skin, but the latter also gradually acquired a dark 

 green colour (PL IV., Fig. 17). All the specimens 

 (some twenty in number) were exactly alike, and 

 showed no trace of marking. 



Second Stage. 



The first ecdysis occurred after 5 6 days, the 

 length of the caterpillars being from nine to ten 

 millimeters. After this first moult they appeared 

 of a shining green, the horn, which was black 

 during the first stage, becoming a little red at the 

 base, while a fine white subdorsal line extended 

 from the horn to the head (Fig. 18). The head 

 and legs were green ; the divisions between the 

 segments appeared as fine light rings, and the 

 entire upper surface of the segments was also crossed 



