Adaptability Irreconcilable with Pre formation 127 



considerably developed tuft of hair to appear on the 

 outside. 93 Would Weismann also presuppose its own 

 determinants for this tuft? And if this tuft arises 

 without being represented in the germ plasm by its own 

 determinants, why cannot the same process occur in 

 normal development for other parts of the organism? 

 Normal and abnormal development do not differ essen- 

 tially from each other; and the causes which produce 

 them are of the same nature in both. 



Weismann certainly recognized the great importance 

 of the capacity of alteration by functional adaptation, 

 possessed by both embryonic and adult organisms. "If 

 this principle did not exist," he writes, "the organism 

 would be like a building, of which each stone is already 

 prepared before the situation and use of the building is 

 determined. Such a predetermined ontogenesis could 

 not produce any organism capable of living. The influ- 

 ences under which organisms exist during their develop- 

 ment are never exactly the same and to be able to 

 adapt themselves to them they must possess a certain 

 freedom." 94 



But we cannot repeat often enough, that this great 

 capacity of adaptation is absolutely irreconcilable with 

 his theory of determinants, or with any preformistic 

 composition of the germ substance. If functional adapta- 

 tion effects "the adjustment of the primary hereditary 

 anlagen, that is of the determinants, to new circum- 

 stances," 95 this signifies that these new circumstances 



88 Dareste: Recherches sur la production artificielle des mon- 

 struosites. P. 327, 538. 



"Weismann : The Effect of External Influences upon Develop- 

 ment. The Romanes Lectures, 1894. P. 16 17. 



"Weismann: Ibid, P. 16. 



