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SHARE OF THE PARENTS IN BUILDING UP THE OFFSPRING 61 



ment beside or upon one another form an extremely complex structure, 

 the id. Ids and determinants are livino; vital unities. Each nucleus 

 contains several, often many, ids, and the number of ids varies with 

 the species and is constant for each. The ids of the germ -plasm of 

 each species have had a historical development, and are derived from 

 the germ-plasm of the preceding lineage of species; therefore ids 

 can never arise anew but onl}^ through multiplication of already 

 existing ids. 



And now, equipped with this knowledge, let us return to the 

 point from which we started, and inquire whether the Lamarckian 

 principle of evolution, the inheritance of functional modifications, 

 must be accepted or rejected. 



