172 



BIOLOGICAL LECTURES. 



is not, therefore, one of a peculiar nature, nor one which in- 

 volves a leading principle, but refers solely to the special process 

 tvhereby the normal form is restored. The same holds good 

 also with respect to the manifestations of the postulated regen- 

 erative-plasma in cases where development is disturbed during 

 the cleavage stages. 



The continuity of typical formation, the contimiity of the typi- 

 cally developed and undeveloped material of formation is, there- 

 fore, not interrupted by these irregular processes, and, no matter 

 how difficult it may be to form a conception of the details of 

 the phenomena, there is still no urgent reason for assuming a 

 metaphysical process. 



'' Incidit in Scyllain, qui vult vitare Chary bdim'' is particu- 

 larly applicable to the investigator in the field of developmental 

 mechanics. The too simply mechanical and the metaphysical 

 conception represent the Scylla and the Charybdis, to steer one's 

 course between which is indeed a difficult task, a task which 

 few have hitherto accomplished. It cannot, however, be denied 

 that the seductiveness of the latter views has been increasing 

 with the increase in our knowledge. 



The least productive method of carrying on developmental 

 mechanics is to start out in the very beginnings of exact inves- 

 tigation from the limited number of facts at our disposal, and 

 to pour forth numerous and long-winded essays on the length 

 to which our understanding can go in this field and on the 

 roles which opposing formative principles play during develop- 

 mental processes. 



It is true that in order to understand the problems before us 

 it was necessary to elucidate more clearly the old contrasts be- 

 tween Evolution and Epigenesis, but this was not for the pur- 

 pose of producing endless theoretical disquisitions, but with the 

 aim of establishing a basis for exact investigation (16). Still we 

 must regard as useful the attempt to bring together all the 

 facts which were supposed to support each of the possible 

 views. Continued discussion, however, and the premature ex- 

 pression and maintenance of final one-sided opinions on these 

 still unknown conditions, can only injure the reputation of our 

 immature investigation along causal lines, and withdraw the 



