650 Studies in Ike Theory of Descent. 



ing of the young stages, and have acquired the 

 brown coloration of the dark surroundings of the 

 insects which conceal themselves by day. In one 

 species this change has now occurred in almost 

 all individuals, in others in only a larger or smaller 

 proportion of them. Now supposing that among 

 these species there occurred one, the physical 

 nature of which did not admit of the production of 

 brown shades of colour, would the species for this 

 reason succumb ? Is it not conceivable that the 

 want of colour adaptation might be compensated 

 for by better concealment, i. e. by burrowing into 

 the earth, or by a greater fertility of the species, 

 or by the development of warning signals sup- 

 posing the species to be unpalatable or finally, 

 by the acquisition of a terrifying marking ? In 

 other words, could not the caterpillar itself modify 

 the new condition of life that of being concealed 

 by day in accordance with variations made 

 possible by its physical nature ? 



As a matter of fact in one of these species the 

 green colour remains unchanged in spite of th< 

 altered mode of life, and this species, wherever i 

 occurs, notwithstanding the persecution of ento- 

 mologists, is always common (Deilephila Hippo- 

 phaes)] it conceals itself better and deeper how 

 ever than those other species which, like Sphinx 

 Convolvidt, are difficult to detect on account oi 

 their brown colour. In another species the striking 

 yellowish green colouring is likewise retained in 



