Weismannism ttp to date (1893). I2 3 



heredity " by the term " molecules." Indeed, in these 

 later volumes he has fully anticipated my remarks 

 touching the use of this term in his previous " Essays 1 ." 

 The result of his more mature reflection may be 

 presented in epitome thus. 



A number of " molecules," in the proper or chemical 

 sense of the word, go to form a " biophore,'' which is 

 the ultimate unit of living substance. 



A number of "biophores" go to form a "deter- 

 minant," which is a special element in the germ-plasm, 

 capable of directing the ontogeny of such and such 

 a group of cells as is independently variable from the 

 germ onwards. 



A number of "determinants " go to form an "id," 

 which is the same hypothetical body as Weismann 

 has hitherto designated by the term " ancestral germ- 

 plasm." That is to say, it is a group of determinants 

 indissolubly united in phylogeny, and therefore 

 transmitted by heredity as one complex whole. Ids 

 are, perhaps, microscopically visible ; and, if so, they 

 probably correspond to the small granules (micro- 

 somata), which are familiar to the histologist in the 

 structure of chromosomes. 



A number of " ids " go to form an " idant," which 

 is a chromosome, or chromatin fibre 2 . 



In my opinion the most important advance which 

 Weismann has made in his theory by means of this 

 scheme has reference to the third of these divisions — 

 the determinant. It is a matter of observation that 

 every cell of a multicelluar organism does not vary 



1 See above, p. 54, note. 



2 See Darwin and after Darzvin, Part I, p. 129. 



