1 68 Studies in the Theory of Descent. 



of in the present essay, this arises entirely from a 

 knowledge of the imperfections in the basis of 

 facts. If however, through the united labours of 

 many investigators, the individual development 

 of all the species of Sphingidce now existing should 

 at some future period be clearly laid before us, 

 we should then not only have arrived at a know- 

 ledge of the relative ages of the different species, 

 genera and families, but we should also arrive at 

 an explanation of the nature of their affinities. 



It is erroneous to assert that Classification has 

 only to take form-relationship into consideration ; 

 that it should and can be nothing else than the 

 expression of form-relationship. The latter is 

 certainly our only measure of blood-relationship, 

 but those who maintain the assertion that form- 

 and blood-relationship are by no means always 

 synonymous, are undoubtedly correct. I shall in 

 a future essay adduce facts which leave no doubt 

 on this point, and which prove at the same time 

 that modern systematists especially in the order 

 Lepidoptera have always endeavoured although 

 quite unconsciously to make the blood-relation- 

 ship the basis of their classification. For this 

 reason alone, larvae and pupae would have an 

 important bearing upon the establishment of sys- 

 tematic groups, although certainly in a manner 

 frequently irregular. 



It must be admitted that so long as we are 

 able to compare the species of one group with 



