analogovs to that of the brain 47 



substance." " May we not therefore consider 

 it probable that the nucleus plays in the cell 

 the part of a central nervous system ? " was 

 the question raised by Dr Francis Darwin 

 in his masterly Presidential Address to the 

 British Association in 1908. I am aware of 

 no smallest detail in which the analogy 

 between the two fails, and — in my opinion 

 at all events — Dr Darwin was amply justified 

 in contending, as Hering in his classic paper 

 had done before him, "that ontogeny — the 

 building up of the embryo — is actually and 

 literally a habit." 



Further, as Dr Darwin goes on to remark, 

 this so-called mnemic theory is " strongest pre- 

 cisely where Weismann's views are weakest — 

 namely in "giving a coherent theory of the 

 rhythm of development." The prodigious 

 complication of Weismann's germ-plasm with 

 its idants ids, determinants and biophores — 



