46o HEREDITY AND DEVELOPMENT 



adjustment of parts — in fact, a struggle. This is often referred 

 to as intra-selection or histonal — i.e. tissue — selection. 



As Weismann says, " The tissues and the parts of the tissues 

 have to distribute and arrange themselves so that each comes 

 to fill the place in which it is most effectively and frequently 

 affected by its specific stimulus — that is, the stimulus in regard 

 to which it is superior to other parts ; but these places are also 

 those the occupation of which by the best reacting parts makes 

 the whole tissue capable of more effective function, and there- 

 fore makes its structure the fittest. . . . The cells which as- 

 similate more rapidly because of the more frequent functional 

 stimulus increase more rapidly, draw away nourishment from 

 the more slowly multiplying cells around them, and thus crowd 

 these out to a greater or less extent " (1904, vol. i. p. 247). 



As Weismann points out, it is impossible at present to give 

 any precise limitation of the respective spheres of personal 

 and histonal selection. The intra-organismal struggle may 

 be, so to speak, the internal adjustment necessary towards a 

 result which the external process of personal selection is bringing 

 about. " The differentiation of the particular kinds of cells 

 is an ancient inheritance, and depends upon personal selection ; 

 but their distribution and arrangement into specially adapted 

 tissues, so far as there is any plasticity at all, depend upon 

 histonal selection." The architecture of every organ is implicit 

 in the germ and must be referred to a long-drawn-out process of 

 personal selection, but the particular local modifications of the 

 architecture may be adjusted by the intra-organismal struggle. 

 And, again, it must be borne in mind that personal selection may 

 put a full stop at any moment to the achievements of histonal 

 selection if they affect the viability of the creature as a whole. 

 A hypertrophied organ may express the organism's internal 

 endeavour to make the best of a new situation, but it may be 

 fatal. 



In so far as a process of intra-organismal struggle is of normal 



