Problems, Concepts and Their History 



21 



tion of the embryo to interference is a prob- 

 lem to which we shall return in the next 

 section. But it may be commented here that 

 Roux, like von Baer, has made a greater ad- 

 vance than Darwin in the descent from 

 metaphysics to the level of the organism; as 

 a result of Roux' program, after all, hy- 

 potheses can be tested by exact investigation 

 — and the investigator need only to read any 

 single paper by Spemann or Harrison to 

 know how exact — in an experimental labora- 

 tory. 



This section was started, it may be re- 

 membered, from the premise that a back- 

 ward look might give a clue as to how to 

 proceed in the future for the best progress 

 of embryology. The primary trend that 

 emerges from the survey has seemed the grad- 

 ual transition from the metaphysical to the 

 physical that characterizes the progress of all 

 developing science. What help may we de- 

 rive, then, from the embryologists who have 

 made the greatest progress in this respect? 



The one valid generalization that can be 

 drawn is that the great progressive minds of 

 embryology — those of Aristotle, Wolff, von 

 Baer, and Roux — and in our own times those 

 of Spemann and Harrison — have been those 

 of the investigators who have learned to ad- 

 dress the embryo by the right question; and 

 these are the men who have derived their 

 intuitions primarily from the study of the 

 embryo itself. The investigators who have 

 derived their ideas from the philosophical 

 side, and examined their embryos to fit their 

 observations into philosophical patterns al- 

 ready set and rigid — Goethe, St. Hilaire, 

 Haeckel, Driesch — were the minds whose 

 philosophical patterns delayed rather than 

 accelerated the course of embryological 

 progress. Aristotle and Wolff and von Baer 

 and Roux started out too from philosophical 

 and theoretical premises, but in such a way 

 that they relegated the initiative of answer- 

 ing their problems to the embryo itself; they 

 could do so only because it was the embryo 

 that gave them their clues as to how to ask 

 their questions. The others had been more 

 interested in the ideas than the embryos, and 

 had become captured by them to the detri- 

 ment both of themselves and science. 



Examining the problem from another as- 

 pect, we may say that the greatest delaying 

 influences on embryology have been first 

 the acceptance of the seventeenth century 

 preformation doctrine, then the doctrines of 



Unity of Type, later the recapitulation doc- 

 trine, all concepts whose philosophical rather 

 than their embryological content insured 

 their success. Are we in the course of under- 

 going a similar delay? Are we too indulging 

 in too high a degree of metaphysical specu- 

 lation, pushing back what we cannot under- 

 stand into concepts of fields and gradients 

 which still have only metaphysical reality 

 and into invisible realms what visible struc- 

 ture only inadequately explains? Is our pres- 

 ent emphasis on the biochemical and bio- 

 physical constitution of the embryo a reac- 

 tion against this? It is now again beginning 

 to be admitted (cf. many authors in Parpart, 

 ed., '49) that the new biochemistry is insuf- 

 ficient to answer our fundamental problem 

 of organization. We can not safely under- 

 estimate the complexity of the problem we 

 attempt to solve, to borrow phraseology from 

 Wheeler (1898). In biological science, struc- 

 ture is inadequate to explain process. As biol- 

 ogists, we are bound to fail when we use 

 methods applicable only to the study of 

 structure for the analysis of processes func- 

 tioning in time. The problem of modern em- 

 bryology as stated above was crudely 

 summed vip as the problem of determining 

 the degree to which particular material an- 

 swers to Roux' description of differ entiatio 

 sui or differentiatio ex alio at any one mo- 

 ment. We have no methods as yet to deal 

 with analyzing the transition from one mo- 

 ment to the next. Here the problem is sim- 

 pler for the classical physiologist, and it is 

 because of this that the progress of the em- 

 bryologist has followed rather than preceded 

 his. 



Another trouble has been, historically 

 speaking, our constant opposition of the 

 metaphysical to the physical; there may be 

 a biological level, too, at which one might 

 work without retreating to the camp of the 

 spiritualists and vitalists, and this is where 

 our imagination has been and still is at its 

 weakest. Roux saw the dilemma, as have so 

 many others (1895c, p. 23): 



Fiir den Forscher auf dem Gebiete der Entwicke- 

 lungsmechanik gilt in hohem Masse das Wort: 



"Incidit in scyllam, qui vult vitare charybdim." 



Die zu einfach mechanische und die metaphysische 

 Auffassung reprasentiren die Scylla und die Cha- 

 rybdis, zwischen welchen dahin zu segeln in der 

 That schwer und bis jetzt nur Wenigen gelungen 

 ist. 



Some of the limitations of the too simply 



