446 Transactions of the Society. 



it is made as well as born. And what is true of an explicit in- 

 dividual, that he makes experiments in self-expression, may be 

 true, for aught we know, of those implicit, telescoped-down in- 

 dividualities which we call germ-cells. In any case, we see no 

 reason to part with th(i idea of the full-grown organism as an 

 agent that shares in its own evolution. 



§ 8. The tendency of modern research has been to lay emphasis 

 on the idea of hereditary particulateness, tiiat the characteristics 

 of organisms are made up of elementary units, without intergrades, 

 as sharply separated from one another as the chemical elements. 

 This is the idea of " unit characters," independently heritable and 

 independently variable. It is very striking that a trivial feature 

 in the hands* — a reduction of the index and middle finger (in spite 

 of the presence of a little extra triangular bone at their bases) 

 and a consequent projection of the ring-finger should behave as a 

 jMendelian character for at least four generations, and be found in 

 fifteen out of thirty-six descendants of the family investigated. 

 There is indirect evidence that particular unit characters are repre- 

 sented by particular particles (factors, determinants, or genes) in 

 the germ-plasm, or perhaps by ultra-microscopic differences of 

 architecture, and the idea works well, like the atomic theory in 

 chemistry. But it has its limitations, and it must not be pressed 

 so hard that we lose sight of the unity of the organism even in 

 the germ-cell phase of its being, and of the fruitful conception of 

 correlated variations. An exaggeration of the idea of particulate- 

 ness leads to a view which is too mechanical to fit living creatures, 

 as if the organism evolved like a machine perfected piecemeal by 

 the adding on of many little patents independent of each other. 

 A reaction may be seen in the recent book by Professor T. H. 

 ]\Iorgan and others on " The ^Mechanism of Mendelian Inherit- 

 ance" (1915), where it is insisted that the so-called unit character 

 is only the most obvious or most significant product of the postu- 

 lated "factor," that the effects of a "factor" may be far-reaching 

 and manifold, and that a single character may depend on many 

 " factors " which interact. " Cases of interaction of factors, in 

 which the effect of one factor is altered by the action of another 

 factor, are very numerous." " The expression of a factor-difference 

 may not be limited to one region, but may produce a different 

 effect in different regions." 



There is much to suggest that we should do well to appreciate 

 afresh the idea which Darwin and Sir Eay Lankester have em- 

 phasized of the " correlation of variations," that one change — as 

 we see, for instance, in disease — may have manifold expressions or 

 outcrops in different parts of the body, that the organism may 

 change as a unity in many parts at once. It is not difficult to 



* H. Drinkwater, Journ. Anat. Physiol., 1. (1916) pp. 177-86 (14 figs.). 



