IDS, DETERMINANTS, AND BIOPHORES 213 



stock, the retention of others in their containing determinants 

 and ids — that determines variation. No two individuals contain 

 identical groups of determinants and identical ids, and, as these 

 control development, therefore no two individuals are identical. 

 If in reversion the characters of an ancestral form, it may be 

 hundreds of generations back, are reproduced, this is because 

 in the process of reduction, followed by fusion, of the two parental 

 germ plasms, the ancestral ids come to predominate to the 

 exclusion or casting out of the ids of more recent generations. 

 Why this should tend to happen in a special order of cases the 

 theory does not venture to explain. 



The reader from these data should be able to apply the theory 

 to particular cases. It has also to be added that Weismann 

 holds that the development of the individual from the ovum 

 proceeds in such a way that by nuclear division it is brought 

 about that the germ cells are assured of possessing a complete 

 set of ids, whereas the body cells do not gain this complete set. 

 There is a qualitative differentiation of the chromatin passing 

 to what are to be the eventual tissues of one or other order, so 

 that ultimately the particular determinants find themselves in 

 control of particular groups of cells, destined to produce specific 

 tissues or parts of tissues. 



There is, we confess, something that savours of mediaeval 

 scholasticism in this conception, something remote from our 

 general conception of the order of natural events, and, as a matter 

 of fact, the whole edifice of ids, determinants, and biophores 

 collapses when confronted with the findings of physical science. 

 Weismann's biophores, in brief, composed as he imagines them 

 of numerous molecules, some of them complex and of large size, 

 must be smaller than are individual atoms ! We can in certain 

 nuclei recognize rows of granules forming the individual chromo- 

 somes — little bodies 0*5 fju or less in diameter — bodies considerably 

 smaller than the micrococci of suppuration. These Weismann 

 regards as the individual ids. Each id is, he postulates, made 

 up of determinants, of which, as each region capable of variation 

 is supposed to be represented by a separate determinant, there 

 must in the human id be thousands rather than hundreds. Each 

 determinant is made up of biophores or ultimate units of living 

 matter ; each biophore, according to him, consists of a group 

 of molecules. Each molecule is, we may add, composed of 



