182 



THE EVOLUTION THEORY 



disposed to think, on this account, that the ancestors of D. Idppoijlia^s 

 bore rings on all the segments, and that these had gradually become 

 vestigial on the majority of them, because they had lost their earlier 

 biological importance, and now, by adaptation to the buckthorn, could 

 only be of use on the second last. But when we take the ontogeny 

 also into account we find in the young caterpillar only a simple 

 sub-dorsal line, upon which, in the third stage, the red spot of the 

 tail-horn segment appears (Fig. 8, A). 



No spots ever occur on the other segments at this stage ; they 

 only appear in the last stage, but as the}^ may be entirely wanting, 

 they must have arisen as the result of internal laws of correlation, 

 that is, they must be recapitulations of the hindmost spots which 

 arose in the phylogeny through natural selection. We may conclude 



^ 2 - 

 ^ ^ 



Fig. 1 1 8. Two stages in the life-history of the Spurge HaAvk-motli (Deilephila 

 euphorbice). A, first stage, the caterpillar dark l)lackish-green, without 

 marking. B, second stage, the row of spots is distinctly connected by a light 

 streak, the vestige of the sub-dorsal stripe. 



this, at least, if we believe in the truth of the fundamental proposition 

 of the biogenetic law, and admit that there is in the ontogeny some 

 more or less distinct recapitulation of the phylogeny. 



This proposition may be recognized as true in the case of Deilephila 

 also, if we compare the different species with one another as regards 

 their ontogeny. We find here too that not only the sub-dorsal, that 

 is, the phyleticall}^ oldest marking of the Sphingid caterpillars, occurs 

 everywhere in the young stages, but also that it is being shunted 

 back to younger and younger stages, in proportion to the degree of 

 the development of the spot-marking reached in the full-grown 

 caterpillar. Thus, for instance, in the caterpillar of Deilepldla 

 eiipliorhioi the highest form of spot-marking is reached, and in this 

 species the sub-dorsal line is no longer the sole marking element at 



