( 450 ) 



Artbildung, the retrogressive development of other characters B, A beginning as 

 minnte individual characters and ending as specific and gronp characters, B beginning 

 as characters common to a number of species, becoming in other species more and 

 more obsolete, and ending as minnte individual characters. Why is it A that 

 demonstrates progressive development ? Why not B ? As A leads from the banded 

 to the not-banded, and B from the not-bauded to the banded wing, why must 

 Evolution necessarily have taken the first direction ? Because, says Eimer {Ortho- 

 genesis, p. 469), 



(4) This cannot be : for " if the species which 1 consider to be the youngest 

 were the phyletically oldest, my figurative tree would be reversed, the branches 

 directed downwards " ; that means that " numerous or almost countless forms 

 would have developed all in the same direction towards a banded form; ... we should 

 have a polyphvlettc tree." — This argument is of course qnite invalid, even if the 

 connection between the forms were really such as Eimer maintains. It is a con- 

 tention of Artbildung that the Lepidoptera develdp in tlie direction from banded to 

 spotted wings : why could one not also contend that the Lepidoptera develop in the 

 direction from spotted to banded wings ? That has surely nothing to do with the 

 question of the mono- or polyphyletic origin of Lepidoptera. The branches of the 

 tree would be divergent, whether the ancestral pattern consisted of continuous bands, 

 or of internervular spots, and in both cases there would also be convergent develop- 

 ment in certain characters. 



(5) But an unconfutable proof, continues Eimer, of the correctness of his opinion 

 is given by the ontogenetic development of the wing-pattern in the wing of the 

 chrysalis. — Fapilio podalirius has, according to Artbildung I., preserved a pattern 

 on the forewing which is similar to that of the ancestral form of the whole order. 

 If this contention is correct, we must necessarily find that in the ontogeny of the 

 wing-pattern of podalirius the first stages are still more ancestral than the pattern 

 of the imago, that the markings appear as bands which then undergo changes 

 leading to the special form of the imago bands ; while, on the other hand, if the 

 bands of podalirius represent j'ounger phyletic stages, we must find that the first 

 ontogenetic stages of the pattern do not consist of bands. Now, what is really found 

 on the pupal wing oi podalirius ? The rudiments of the pattern of the forewing of 

 pod/dirius in the jmpa arc, according to Haase and Countess Linden, iutcrncrvular 

 spots, which then fuse to bands. Ontogeny, therefore, does not j)rove what it is 

 said in Orthogenesis to have proved. 



The second general result of Artbildung which is of greater importance for 

 classification is that in various forms (wliich do not stand in the connection of 

 ancestor and descendant) a new character may appear which was not present in the 

 common ancestor, and that we consequently meet with similar forms in not closely 

 allied groups, forms the similarity of which is due not to immediate relationship, 

 but tu similarity in the direction of development, to Homoeogenesis. I fully 

 acknowledge that it is a great merit of Artbildung to bring to mind again and 

 again that similarity is not always a sure sign of relationship. But if one recognises 

 the bearing of this result on classification, one should be doubly careful in accepting 

 similarity in one organ, in the pattern of the wing, as evidence of relationship, with- 

 out, I'urtlier innuiry whether the assumed relationslup is borne out by other organs. 

 Homoeogenesis sliows distinctly that a classification built up on one character or on a 

 set of correlatively mutating characters has no sound basis. I leave it to the reader 

 to consider whether there was a priori any great probability that the researches 



