206 Studies in the Theory of Descent. 



In this last stage also there is great variability 

 of colour, but although each particular character 

 is subject to fluctuation, the individuals of the same 

 brood show but little variation among themselves. 21 

 Thus, the dorsal line is sometimes black, and 

 sometimes red, or again, this colour interrupted 

 with black, so that only small red spots mark its 

 course. The head may be entirely red, or this 

 colour mixed with black. On the under side of 

 the caterpillar, red generally predominates, but in 

 some specimens this is replaced by black. The 

 ground-colour is also variable, being generally 

 a shining brownish-black, but sometimes dull 

 coaly black. The shagreen-dots are sometimes 

 white and sometimes yellow, and the " mirrors" of 

 the ring-spots are also often yellowish. 



The most interesting variation, however, appears 

 to me to be the following : In many specimens 

 from Kaiserstuhl (Breisgau), the red was unusually 

 vivid, and was not limited to the ordinary places, 

 but occupied also the triangles on the posterior 

 edges of the segments (Fig. 44), which are green 

 in the third and fourth stages (Fig. 42). This 

 variety has also been figured by Htibner. In 



21 Upon this fact obviously depends the statement of that 

 extremely accurate observer Rosel, that the caterpillar of 

 Euphorbia is but very slightly variable ("Insektenbelusti- 

 gungen," Bd. iii. p. 36). I formerly held the same opinion, till 

 I convinced myself that this species is very constant in some 

 localities, but very variable in others. It appears that local 

 influences make the caterpillar variable. 



