276 Stiidies in the Theory of Descent. 



volutions again are smooth, and the author believes 

 (on other grounds) that the more remote pro- 

 genitor possessed a smooth shell. 



In this case therefore, and in that of the am- 

 monites, every shell to a certain extent proclaims 

 the ancestral history of the species ; in one and the 

 same shell we find different phyletic stages brought 

 into proximity. The markings of caterpillars do 

 not offer similar facilities ; nevertheless I believe 

 that by their means we are led somewhat further, 

 and are able to enter more deeply into the causes 

 underlying the processes of transformation, be- 

 cause we can here observe the living creature, and 

 are thus enabled to study its life-history with more 

 precision than is possible with a fossil species. 



When, in 1873, I received Wiirtemberger's 

 memoir, I was not only struck with the agree- 

 ment of his chief results with those which I 

 had arrived at by the study of larval markings, 

 but I was almost as much astonished at the great 

 difference in the interpretation of the facts. The 

 latter indicate the gradual backward transference 

 of a new character from the latest to the earlier 

 ontogenetic stages. Without further confirmation 

 Wiirtemberger assumes that it is to a certain 

 extent self-evident that the force producing this 

 backward transference is the same as that which, 

 according to his view, first called forth the charac- 

 ter in question in the last stage, viz., natural se- 

 lection. " Variations acquired at an advanced 



