44 HEREDITY AND SELECTION IN SOCIOLOGY 



Similarly with those remarkable cases of adaptation to their 

 environment exhibited by certain butterflies, which adapt 

 themselves to the colour of the leaves of the trees in which they 

 habitually live. There are certain species of insects one race 

 of which lives in woods, another in the fields, and the colour of 

 both has been difEerentiated in harmony with their surroundings. 

 The influence of external conditions! is here obvious ; but only 

 certain parts of the organism have been modified, not the whole, 

 as would have been the case had the germinal substance been 

 homogeneous. That only certain parts should have been 

 modified shows that the germinal substance contains certain 

 autonomous living particles, whose modification entails the 

 modification of these parts, to which they stand in definite 

 developmental relation. 



We have no knowledge of the forces which determine the 

 composition of the biophors, or which lead to the histological 

 diflerentiation of the ceU. But the biophors which transform 

 the undifferentiated embryonic cell into the highly differentiated 

 tissue-cell must themselves possess a very specific and highly 

 differentiated nature ; they must be able to determine the specific 

 nature of the cell into which they penetrate, and they must be 

 capable of securing the continuity of the pecuhar substance — 

 whether of nerve or muscle or gland — ^which comes down from 

 the preceding generation, for we cannot suppose continually 

 repeated series of re-creations of such complicated substances. 



In his theory of. germinal selection, advanced for the first 

 time in 1892, Weismann has admittedly overcome the great 

 majority of objections raised against his original theory of the 

 ancestral plasm. Even the French critics, who are more preju- 

 diced than others against the views of the great antagonist of 

 Lamarck, have admitted jthis.^ - Formerly the objection against 

 the theory of the ancestral plasm was a serious one. On the 



1 Cf. Yves Delage, L'Heridite et les grands ProlUmes de la Biologie 

 ginirale, p. 558. Paris, 2nd edition, Schleicher, 1903. 



