THE GASTllAEA-THEORVj ETC. 241 



of the animal kingdom," and sees in them, Avith Keferstein 

 and others, the " most brilliant confutation of the Darwinian 

 heresy," and the strongest argument against the truth of the 

 theory of descent. 



This last point our adversaries have themselves, without 

 foreseeing it, pointed out as the Achilles' heel of the theory 

 of types. For it is quite certain that the theory of types, in 

 the original sense of its authors, does, without doubt, stand 

 in a fundamental contradiction to the theory of descent. 

 This contradiction lies not so much in this that the ty))es 

 are considered as completely independent and separate higher 

 groups of the animal kingdom, but rather in the teleogical 

 principal of their conception. The idea that the types form 

 entirely independent groups of forms is of course inconsistent 

 with any monophyletic conception of the animal kingdom, 

 which traces all animals as descendants from a single com- 

 mon root-form ; but it would allow itself to be brought 

 into unison with the theory of descent in this that one 

 requires for each type an independent stem-form, conse- 

 quently the entire animal kingdom requires a polyphyletic 

 descent — so many types, so many phyla. The conception of 

 the immanent original " plan of structure of the types," 

 w'hich forms the true teleogical ground principle of the 

 theory of types, is, on the contrary, perfectly inconsistent 

 Avith the theory of descent. 



As soon, therefore, as the theory of descent reformed by 

 Darwin attacked the Baer-Cuvier theory of types, it com- 

 pelled the latter to defend itself by, first, freely giving up its 

 teleogical ground principle, and, secondly, at the same time, 

 the connectioir of the types with one another had to be 

 modified. The first attempt towards this I made in 1866 

 in my ' General History of Development ' (" General Mor- 

 phology ,'' 2nd volume, chapters xvi, xix, xxiv, and xxv). 

 First, 1 have there already pointed out that Baer's type of 

 development is nothing further than the consequence of in- 

 heritance, and Baer's grade of improvement is nothing further 

 than the consequence of adaptability (1. c, p. 11) ; therewith, 

 on the one side, the dualistic notion of types or the teleogical 

 plan of structure is brought back to the mechanical prin- 

 ciple of inheritance (consequently to the physiological func- 

 tion of increase), 1. c, p. 171 ; on the other hand, the dualistic 

 idea of perfection or the teleogical aim of increase is conse- 

 quently reduced to the mechanical principle of adaptability, 

 that is, to the physiological function of nutrition (1. c, p. 

 193). Secondly, I have, then, already shown that the 

 different higher types of the animal kingdom can be only 



