414 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



Going back to an early and nut generally known work of Weis- 

 mann, Upon the Final Causes of Transmutations, 1 I found that the 

 origin of his teachings was not experimental; it was theological. 

 In 1876 Weismann was still a Darwinist. His own experiments on 

 seasonal dimorphism had confirmed the facts discovered by Dorf- 

 meister concerning the effects of temperature in producing two dif- 

 ferent races of butterflies, while the experiments that Weismann made 

 subsequently on mice to prove the nontransmission of a mutilation — 

 the clipped tail — added absolutely nothing to our previous knowl- 

 edge. If Weismann had taken the trouble of consulting Darwin's 

 Variation before he had written his eighth essay he would have seen 

 that clipped tails are not inherited, and he would have learned why 

 such mutilations have little chance of being inherited — embryonal 

 regeneration — and why their nontransmission did not affect Darwin's 

 views upon the inheritance of variations. 



It was under the influence of Schopenhauer's, Hartmenn's, and 

 Karl Baer's criticisms of the philosophical substance of Darwinism 

 that Weismann accepted the idea of Baer that evolution without a 

 teleological guidance from above was an unscientific conception. He 

 thus came to the conclusion that, although evolution is a mechanical 

 process, it must have been predetermined by a supreme power in 

 accordance with a certain plan. And, in order " to reconcile teleology 

 with mechanism," he borrowed from Nageli and partly from Nuss- 

 baum the idea of " continuity " of the germ plasm ; and thus he came 

 to a Hegelian conception of an " immortal germ plasm " — " a matter 

 endowed with an immortal soul." His hypothesis was thus suggested 

 by those same considerations, lying outside the domain of science, 

 that Darwin had had to combat. 



In his Essays upon Heredity, written in 1881-1887, Weismann 

 represented his germ-plasm hypothesis as an outcome of the remark- 

 able microscopical discoveries made in those years by a number of 

 well-known anatomists concerning the processes taking place during 

 and immediately after the fertilization of the egg. But as early as 

 1897 Prof. Hartog made the quite correct remark that the cardinal 

 defect of the theory of Weismann was its " objective baselessness." 



It professes [he wrote] to be founded on the microscopic study of the changes 

 in the nucleus in cell division, but there we find nothing to justify the assump- 

 tion of two modes of nuclear division in the embryo — the one dividing the deter- 

 minants and the other only distributing them between the daughter cells. - 



Later on two of the leading microscopists who took part in the 

 just-mentioned discoveries, far from giving support to Weismann's 



1 " Ueber die letzten Ursachen der Transmutationen," in Studien zur Descendenztheorie, 

 Leipzig, 1876, chapter " Mechanismus und Teleologie." I don't know whether there 

 exists an English translation of this chapter. 



2 " The Fundamental Principles of Heredity, " in Natural Science, xi, October and No- 

 vember, 1897. Reproduced in Professor Marcus Hartog's Problems of Life and Reproduc- 

 tion, London, 1913. 



