296 Studies in the Theory of Descent. 



with great difficulty. After the third moult they 

 become brown, and can be easily seen when at 

 rest on their food-plant. 



Now in all known caterpillars brown colours are 

 adaptive, sometimes causing a resemblance to the 

 soil, and at others to dead leaves or branches. As 

 soon, therefore, as the caterpillars have attained 

 a considerable size, they remain concealed by day. 7 

 The truth of this observation not only appears 

 from various entomological notes, but I have 

 frequently convinced myself of its accuracy. I 

 well remember from the earliest times that C. 

 Elpenor, especially when the larva is adult, always 

 rests by day among the dead branches and leaves 

 of its shrub-like food-plant, Epilobium Hirsutum ; 

 and even when this species lives on the low-grow- 

 ing Epilobium Parviflorum, it conceals itself by day 

 on the ground, among the tangled leaves and 

 branches. I have observed that Sphinx Con- 

 volvuli has a precisely similar habit, for which 

 reason it is difficult to obtain, even in localities 

 where it occurs very commonly. 



In the neighbourhood of Basle I once found at 

 mid-day a brown caterpillar of Pterogon CEnotherce 

 on an isolated dead branch of Epilobium Rosmari- 

 nifolium, and I was informed by H err Riggenbach- 

 Stahelina collector of great experience who 

 accompanied me that these caterpillars always 

 rest (by day) on withered plants as soon as they 

 7 [See also preceding note 5, p. 294. R.M.] 



