Adaptability Irreconcilable with Preformation 127 
considerably developed tuft of hair to appear on the 
outside.°* 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.” %* 
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,” °° this signifies that these new circumstances 
°2Dareste: Recherches sur la production artificielle des mon- 
struosités. P. 327, 538. 
‘Weismann: The Effect of External Influences upon Develop- 
ment. The Romanes Lectures, 1894. P. 16—17. 
*85Weismann: Ibid, P. 16. 
