The Origin of the Markings of Caterpillars. 295 



the manner in which the di- and polymorphism 

 of caterpillars can be explained from the external 

 phenomena which they present, these phenomena 

 being well adapted for showing the great impor- 

 tance of protective colouring to the larvae. We 

 have here presented a double adaptation, although 

 not quite of the nature of that which I formerly 

 admitted on hypothetical grounds. 6 In the first 

 place, from the developmental history there results 

 the conclusion that all Sphinx-larvae which, in the 

 adult state, are di- or polymorphic, are unicolorous 

 when young. Thus, the caterpillars of Chtzro- 

 campa Elpenor all remain green till the fourth 

 stage, when they mostly become light or dark 

 brown, and only very seldom retain their green 

 colour. Chcerocampa Porcellus behaves in a 

 precisely similar manner ; as also does Pterogon 

 (Enotherce, which inhabits the same localities, and 

 is found on the same food-plant, but is not very 

 closely related to the Chczrocampa. In this 

 species also (P. (Enothercs) the brown is more 

 common than the green form in the adult state, 

 both varieties showing a complicated marking. 

 The young larvae possess only a light green 

 colour, and a pure white subdorsal line as the only 

 marking ; they are so well adapted to the leaves 

 of their food-plants, Epilobium Hirsutum, and E. 

 Rosmarinifolium, that they can only be detected 



See the essay " Uber den Einfluss der Isolirung auf die 

 Artbilding." Leipzig, i 8 7 2, p. 22. 



