4 1 4 Studies in the Theory of Descent. 



Cyparissias generally grows on arid soil which is 

 poor in vegetation, and which therefore affords no 

 concealment, and furthermore, because a cater- 

 pillar, as long as it continues to feed, cannot, and 

 as a matter of fact does not, ever wander far from 

 its food-plant. A habit of concealment by bury- 

 ing in the earth also, such for example as occurs 

 in Acherontia Atropos, could not be acquired by 

 D. Euphorbia, because its food-plant generally 

 grows on hard, dry, and stony ground. 



In addition to these considerations, the foes 

 would be different according as the caterpillar 

 lived on plants which formed dense thickets 

 covering large extents of the shore (Hippophae), or 

 grew isolated on dry hillocks and declivities where 

 the herbage was scanty or altogether absent ; or 

 again, according as the insect, in conjunction with 

 such local differences, fed by day or had acquired 

 the habit of feeding only by night. It must in fact 

 be admitted that new and improved adaptations, 

 or, in more general terms, that inducements to 

 change, when depending on the environment, must 

 be more frequently dissimilar for larvae than for 

 the imagines. We must accordingly expect to find 

 actual change, or that condition of variability which 

 may be regarded as initiative to change, occurring 

 rt^ore commonly in larvae than in perfect insects. 



Since facts are in complete accordance with the 

 resuks of these a priori considerations we may also 

 venture to conclude that the basis of the consider- 



