Problems, Concepts and Their History 



19 



larly, also, he was influenced in the direction 

 of the new preformationism by Weismann. 

 For the new embryology, strangely enough, 

 received a strong impetvis from the old pre- 

 formation as this was revived in a new form. 

 Radl ('30, p. 263) has made the clever com- 

 ment, and justly so, that "Haeckel silenced 

 von Baer, the embryologist, and returned to 

 the ideas of Meckel. Weismann ignored [von] 

 Baer, the epigeneticist, and went back to the 

 idea of the tedious and insipid Bonnet." Roux 

 derived his parentage from them both; and 

 Weismann himself had been, after all, a stu- 

 dent of Leuckart's. 



It is always tempting to contrast Roux' 

 mechanistic preformationist tendencies with 

 the vitalistic and epigenetic interpretations 

 of Driesch, and to assume the enthvisiasm for 

 the new experimental embryology as arising 

 out of the clear-cut difference between them, 

 and as demanding the collection of new evi- 

 dence to justify the choice between them. But 

 what was more influential in starting the 

 new experimental embryology on its way 

 was not the opposition of results and inter- 

 pretations of Roux and Driesch so much as 

 the desire to verify or refute the Roux- 

 Weismann hypothesis that the qvialitative 

 distribution of nuclear material is responsi- 

 ble for the mosaic sort of differentiation 

 which Roux thought he could demonstrate; 

 and the attack begun on it by Driesch and 

 Hertwig in 1892 not only represented the 

 beginning of all the active experimentation 

 to follow, but led directly to the constriction 

 experiments of Spemann which were destined 

 to have such momentous results. 



In the same measure as Weismann was in- 

 directly responsible for the new embryology 

 to follow, nineteenth century materialism 

 lay behind it. Weismann was no freer than 

 any other from the influence of his times; his 

 idioplasm is a modification of that of Nageli 

 which was "like a microscopic picture of the 

 macroscopic individual" (cited from Radl, 

 '30, p. 226). Atomicity, as elucidated by 

 Dalton for chemistry, was implicit in the 

 biological ideas of Mendel and Pasteiir, and 

 equally in the determinants postulated by 

 Weismann. Weismann's contribution, like 

 that of so many influential figures in the 

 history of science, was the expression of his 

 doctrine to a century philosophically ripe 

 for its acceptance. 



And once more a new tool coiild be ex- 

 ploited to make visibly manifest concrete 

 evidence of a theory bound to become popu- 

 lar because of its appropriateness to the de- 

 mands of its times. Now, it was the improved 



achromatic lens, which brought out the cyto- 

 logical details of nuclear behavior during 

 mitosis and meiosis and fertilization, and 

 which gave new meaning to the relationship 

 between cellular inclusions and cellular 

 differentiation, and thus evoked a new in- 

 terest in the old preformation. This had its 

 effect not only on Roux among the em- 

 bryologists. In a way, the work of Whitman 

 and all his disciples who devoted themselves 

 to the study of cell lineage in eggs with 

 determinate cleavage grew out of the same 

 background as Weismann's, and came in a 

 different way to setting vip the premises for 

 a new kind of preformation (see especially 

 Whitman, 1894a, 1894b, and Wheeler, 1898, 

 for brilliant expositions of the fin de sieclc 

 position against the older historical back- 

 ground). It led too to the magnificent work 

 of Boveri, who on a pvu-ely embryological 

 basis established as soundly as the geneticists 

 later the role of qualitative and quantita- 

 tive distribution of the chromosomes. 



Weismann, however, and the new mate- 

 rialism and the new preformationism, and 

 Goette and His and Haeckel were not the 

 only influences to culminate in Roux. He 

 had his ideas from the botanists, too, and 

 not only indirectly as in the case of Nageli's 

 idioplasm adopted by Weismann. Sachs, who 

 was also greatly influenced by Nageli, had 

 been experimentalizing plant biology as Roux 

 was to do with embryology; with the physi- 

 ologists' primary interest in irritability he 

 worked out the basis of what was later to 

 culminate with Loeb in the theory of trop- 

 isms, a concept which the embryologists 

 adopted as soon as the physiologists, and 

 nerhaps with even greater frviit. Roux, in the 

 first paper, after the introduction, pviblished 

 in the new Archiv (1895d), took it over in his 

 use of "cytotaxis" and "cytotropism" as ex- 

 planatory of the relationships of amphibian 

 blastomeres to one another. And Roux was 

 not the only one to employ it: Driesch called 

 in "taktische Reizbarkeit" to explain certain 

 behavior of the mesenchyme cells in the 

 echinoderm embryo. Herbst elaborated it 

 further for embryology, even going so far, in 

 his Formative Rrize in der tierischen Onto- 

 genese, as to postulate on a theoretical basis 

 the dependence of the development of the 

 vertebrate lens on the optic cup, the veru 

 year that Spemann (who had himself learned 

 botany from Sachs) was to perform his first 

 experiment demonstrating it (thoup;h inde- 

 pendent of Spemann; cf. Spemann, '03, p 

 566). The ideas of progressive differentiation 

 which had been developing since Aristotle 



