272 Studies in the Theory of Descent. 



appears in Elpenor in the second stage, whilst in 

 Porcelhis it is present during the first stage. If 

 this line were acquired by the young larva for 

 adapting it at this age to special conditions of life, 

 it should appear in both species at the same 

 stage. Since this is not the case, we may con- 

 clude that it is only an inherited character derived 

 from the adult ancestor of the two species, and 

 now relegated to the young stages, being (so to 

 speak), pushed further back in one species than in 

 the other. 



But the strongest, and, as it appears to me, the 

 most convincing proof of the purely phyletic sig- 

 nificance of the young larval markings, is to be 

 found in the striking regularity with which these are 

 developed in a similar manner in all allied species, 

 howsoever different may be their external condi- 

 tions of life. In all the'species of the Chczrocampa 

 group (the genera Ck&rocampa and Deilephila] the 

 marking no matter how different this may be in 

 later stages arises from the simple subdorsal line. 

 This occurs even in species which live on the most 

 diverse plants, and in which the markings can be 

 of no biological importance as long as the larvae 

 are so small as to be only visible through a lens, 

 and where there can be no possible imitation of 

 leaf-stalks or veins, the leaves and caterpillars 

 being so very distinct. 



Moreover, when in the Macroglossiita (the 

 genera Macroglossa, Pterogon, and Thyreus) we 



