298 Studies in the Theory of Descent. 



throughout its whole life, remaining of a greyish 

 green, which exactly matches the colour of the 

 leaves of its food-plant, Hippophae Rhamnoides. 

 Nevertheless this species also possesses the habit 

 of feeding only at night as soon as it has attained 

 to a considerable size, hiding itself by day at the 

 root of its food-plant. Collectors expressly state 

 that this larva can scarcely be found by day, and 

 recommend that it should be sought for at night 

 with a lantern. 



From the foregoing facts and considerations it 

 may fairly be concluded, that the habit of hiding 

 by day, possessed by these and other allied cater- 

 pillars, was acquired when they resembled the 

 leaves in colour, and that the adaptation to the 

 colour of the soil, or dead foliage and withered 

 branches, ensued as a secondary consequence. 



But why have these caterpillars acquired such a 

 habit, since they appear to be perfectly protected 

 by their resemblance in colour to the green leaves ? 

 The answer to this question is easily given when 

 we consider in which species this habit generally 

 occurs. 



Does the habit prevail only among the species 

 of the one genus Deilephila, and in all the species 

 of this genus ? This is by no means the case, 

 since, on the one hand, many species of Deilephila^ 

 such as D. Euphorbia, Galii, Niccea, and Dahlii, 

 do not possess the habit, and, on the other hand, it 

 occurs in species of other genera, such as Macro- 



