36 The Direction of Evolution 



This impulse is definite enough in many cases, where the 

 conditions do not require accommodation and modification ; 

 but where these demands are urgent upon it, it is surprising 

 what transformations it may undergo. Recent results of 

 embryological and morphological research have proved 

 this so clearly that a school of biologists, called by Delage 

 * Organicists,' 1 has arisen, who place the emphasis in all 

 evolutionary change upon the necessity of the organism, 

 and of its particular organs, to become what they are 

 stimulated to become under the stress of the environment, 

 or, failing to meet these requirements, to die in the attempt. 

 This suggests an important modification of the strictly 

 ' Preformist ' view, made extreme in the earlier writings of 

 Weismann, according to which the accommodations of the 

 individual organism are of no importance, being simply the 

 unfolding of what is preformed in the germ. For even if 

 we admit, as we may, the non-inheritance of acquired 

 characters, we may still hold the general view of the 

 organicists, and also maintain that the hereditary impulse 

 becomes more and more unformed^ rather than preformed, 

 as we advance in the animal scale; each succeeding genera- 

 tion through its own development, in its own life history, 

 making more of the essential accommodations which give 

 it its generic and specific characters. This Weismann has 

 lately in part recognized, in his theory of ' intra-selection ' 

 built up upon the views of Roux. 



Third, if these be the safe results of research in the 

 sphere of development, we then have certain additional 



1 ' The Organicists oppose [to other theories] the combination of a mod- 

 erate predetermination with the continually acting and necessary forces of the 

 environment, which are not simple conditions alone, but essential elements in 

 the final determination.' (Delage, La Structtire du Protoplasma, p. 720. 

 Delage's personal views are cited in Chap. XIII. 3, below.) 



