. 529 



Retention of the Subdorsal Line by Occllated Larva. It 

 has already been shown with reference to the eye-spots 

 of the Chtcrocatnpa-l&rvx, that these markings have been 

 developed from the subdorsal line.and that, in accordance 

 with their function as a means of causing terror, this line 

 has in most species been eliminated in the course of the 

 phylogeny from those segments bearing the eye-spots 

 in order to give full effect to the latter (see p. 379). In 

 accordance with the law that a character when it has 

 become useless gradually disappears, the subdorsal is 

 more or less absent in all those species in which the ocelli 

 are most perfectly developed ; and it can be readily 

 imagined that in cases where adaptation to the foliage 

 exists the suppression of this line would under certain 

 conditions be accelerated by natural selection. On the 

 other hand, it is conceivable that the subdorsal line may 

 under other conditions be of use to a protectively 

 coloured occllated species by imitating some special 

 part of the food-plant, under which circumstances its 

 retention would be secured by natural selection. 



Such an instance is offered by Chatrocantpa Capensis, 

 Linn. ; and as this case is particularly instructive as like- 

 wise throwing light upon the retention of the subdorsal 

 by certain species having oblique stripes (see p. 377, and 

 note 7, p. 378), I will here give some details concerning 

 this species which have been communicated to me 

 by Mr. Roland Trimen, the well-known curator of the 

 South African Museum, Cape Town. The caterpillar of 

 C. Capensis, like so many other species of the genus, is 

 dimorphic, one form being a bright (rather pale) green, 

 and the other, which is much the rarer of the two, being 

 dull pinkish-red. Both these forms are adapted in colourto 

 the vine on which they feed, the red variety according to 

 some extent with the faded leaves of the cultivated vines, 

 but to a greater extent with the young shoots and under- 

 side of the leaves of the South African native vine (Cissns 



M m 



