The Origin of the Markings of Caterpillars. 323 



even during the night ; i.e. in a light so faint that 

 feeble colours would produce scarcely any effect. 

 The bright blue of A cherontia A tropos, for example, 

 would give the impression of oblique shadows 

 without any distinctive colour. 



It is precisely the case of this last caterpillar, 

 which formerly appeared to me to present insur- 

 mountable difficulties to the explanation of the 

 coloured stripes by adaptation, and I believed 

 that this insect would have to be classed with 

 those species which are brightly coloured because 

 they are distasteful, and are avoided by birds. 

 But although we have no experiments on this 

 point, I must reject this view. Unfortunately, we 

 know scarcely anything of the ontogeny of this 

 caterpillar ; but we know at least that the young 

 larvae (stage four) are greener than the more 

 purely yellow ones of the fifth stage (which, how- 

 ever, are also frequently green), and we know 

 further that some adults are of a dark brownish 

 grey, without any striking colours. From analogy 

 with the dimorphism of the species of Charocampa 

 and Sphinx, fully considered previously, it must 

 therefore be concluded that in this case also, a 

 new process of adaptation has commenced that the 

 caterpillar is becoming adapted to the soil in and on 

 which it conceals itself by day. 4 An insect which 



4 The geographical distribution of the dark form indicates 

 that in the case of this species also, the form referred to is 

 replacing the yellow (green) variety. Whilst in the middle of 



Y 2 



