1 86 Studies in the Theory of Descent. 



the appearance of a little brown on the under edge 

 of the foremost of the white spots, this coloration 

 gradually increasing in extent and in depth. At 

 the same time both spots become more sharply 

 distinguishable from the subdorsal line, which 

 becomes constantly greener (Fig. 27). The brown 

 colour soon grows round the white of the front 

 eye-spot, which becomes so far perfected ; whilst 

 the completion of the hind spot is effected slowly 

 afterwards. The formation of the eye-spots does 

 not therefore proceed any more rapidly in this 

 species than in C. Elpenor. 



At the end of the present stage the length of 

 the caterpillar is about four centimeters ; the ground 

 colour is still sea-green ; the subdorsal line is much 

 diminished, completely fading away at its lower 

 edge, but remaining sharply defined above, against 

 the green ground-colour (Fig. 26). 



Fourth Stage. 



After the third moult all the caterpillars (5) 

 became brown, this change occurring therefore one 

 stage earlier than is generally the case with C. 

 Elpenor. In single instances the brown colour 

 appeared in the third stage. The subdorsal line 

 had disappeared from all the segments but the three 

 first and the last. The eye-spots now rapidly 

 attained complete development ; they contained a 

 black pupil, and gave the insect a truly repulsive 

 appearance when, on being threatened by danger, 



