GEEMIXAL SELECTION 157 



We certainly ought not to conclude from the fact that we 

 cannot see into the structure and requirements and methods of 

 nutrition of a very minute mass of substance that its nutrition 

 cannot be unequal, and that it cannot, by its inequalities, give rise 

 to very material differences, especially wlien we are dealing with 

 a substance to which we must attribute an extraordinarily complex 

 organization built up of enormous numbers of extremely minute 

 particles. That this complexity is undeniable is now admitted by 

 many who formerly thought it possible to believe in the simple 

 structure of the germ-substance. How complex not only the germ- 

 substance but every cell of a higher organism is in its structure, 

 and how far below the limits of visibility its differentiations and 

 arrangements reach, is pressed upon our attention by the most recent 

 histological researches, such as those we owe to Heidenhain, Boveri, 

 and many others. The whole scientific world was amazed when 

 it came to know the mysterious nuclear spindle in the seventies, 

 and since then this has been quite thrown into the shade by the 

 discovery of the centrosphere, the centrosome, and more recently 

 even the centriole. and now we believe that these marvellous centres 

 of force may, or must, possess their own dividing apparatus! In 

 the face of discoveries like these no one is likely to be able to persist 

 in recognizing as existing only what is disclosed or even hinted at by 

 the most powerful lenses ; no one can any longer doubt that far below 

 the limit of \'isibility organization is still at the basis of life, and that 

 it is dominated by orderly forces. To me, at least, it seems more 

 cogent to argue from the phenomena of heredity and variation to 

 an enormous mass of minute vital units crowded together in the 

 narrow space of the id, than to argue from the calculated size of 

 atoms and molecules to the number which we are justified in assuming 

 to be present in an id. In my book on the germ-plasm I made 

 a calculation of this kind, and I arrived at figures which seemed 

 rather too small for the requirements of the germ-plasm theory. 

 This has been regarded as a proof that I disregard the facts for 

 the sake of my theory, but it should rather be asked whether the 

 size of the atoms and molecules is a fact, and not rather the very 

 questionable result of an uncertain method of calculation. Un- 

 doubtedly modern chemistry has established the relative weight- 

 proportions of the atoms and molecules with admirable precision, 

 but it can make only very uncertain statements in regard to the 

 absolute size of the ultimate particles. It is therefore admissible 

 to assume that these have a still greater degree of minuteness when 

 the facts in another domain of science require this. 



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