306 THE ORGANISM AS AN HISTORICAL BEING 



" That a notochord should develop out of the archenteric 

 wall because a supporting axis would be beneficial to the 

 animal may be a teleological assumption, but it is at the 

 same time an evolutional heresy. It would never be 

 fruitful to try to connect the different variations offered, e.g., 

 by the nervous system throughout the animal kingdom, if 

 similar assumptions were admitted, for there would be then 

 quite as much to say for a repeated and independent origin 

 of central nervous systems out of indifferent epiblast just as 

 required in each special case. These would be steps that 

 might bring us back a good way towards the doctrine of 

 independent creations. The remembrance of Darwin's, 

 Huxley's, and Gegenbaur's classical foundations, and of 

 Balfour's and Weismann's brilliant superstructures, ought to 

 warn us away from these dangerous regions " (p. 644). 



This same prejudice lies at the root of the idea of 

 Functionswechsel, in spite of the general functional orien- 

 tation of that idea. 



Dohrn's constant assumption is that Nature makes shift 

 with old organs wherever possible, instead of forming new 

 ones. He derives gill-slits from segmental organs, fins and 

 limbs from gills, ribs from gill-arches, and so on, instead of 

 admitting that these organs might quite as well have arisen 

 independently. He objects on principle to the origin of 

 organs de novo. Thus, rebutting the suggestion that certain 

 organs which are not found in the lower Vertebrates might 

 have arisen as new formations, he writes: "Against this 

 supposition the whole weight of all those objections can be 

 directed that are to be brought in general against the 

 method of explanation which consists in appealing without 

 imperative necessity to the Dens c.v niacJiina, ' New forma- 

 tion,' which is neither better nor worse than Gcucmtio 

 cijnivoca" (p. 2l). 



Of a similar nature was the objection to convergence. 1 



Why, we may ask, were morphologists so unwilling to 



1 The importance of convergence came to be realised after the 

 \o.Mie of phylogenetic speculation had passed see Fricdmann, Die 

 Konvergenz der Organismeri) l'-crlin, 1904, and A. Willey, Convergence in 

 Evolution, London, 1911. Also L. Vialleton, Elements dc morphologic 

 des I'ertcbrcs, Paris, 1912. 



