300 Studies in the Theory of Descent. 



remains green throughout its whole larval exist- 

 ence ; and no less from the green forms of the adult 

 larvae of Sphinx Convolvuli, Chcerocampa Elpenor, 

 and Force ilus, all of which conceal themselves by 

 day in the same manner as their brown allies. 



It may be objected that there are Sphinx-larvae 

 instances of which I have myself adduced 

 which live on low small-leaved plants, and which 

 nevertheless do not hide themselves by day. This 

 is the case with the spurge-feeding D. Euphorbia, 

 so common in many parts of Germany. This 

 caterpillar must, however, be classed with those 

 which, on account of their distastefulness, or for 

 other reasons to be subsequently considered, are 

 rejected by birds and other larger foes, and which, 

 as Wallace has shown, derive advantage from 

 being coloured as vividly as possible. I shall 

 return to this subject later, when treating of the 

 biological value of special markings. 



On the other hand, it is readily conceivable that, 

 from the conditions of life of caterpillars living on 

 trees or shrubs with dense foliage, the habit of 

 resting by day and descending from the tree for 

 concealment would not have been acquired. Such 

 larvae are sufficiently protected by their green 

 colour among the large and numerous leaves ; and 

 I shall have occasion to show subsequently that 

 their markings increase this protective resem- 

 blance. 



The di- or polymorphism of the larvae of the 



