164 Evolution and Adaptation 
Weismann continues: “ But the question remains, w/y is 
this the fact?” He believes his hypothesis of the existence 
of determinants in the germ gives a satisfactory answer to 
this “why.” ‘“ According to this theory every independent 
and hereditarily variable part is represented in the germ by 
a determinant, whose size and power of assimilation corre- 
sponds to the size and vigor of the part. These determinants 
multiply as do all vital units by growth and division, and 
necessarily they increase rapidly in every individual, and the 
more rapidly the greater the quantity of the germinal cells 
the individual produces. And since there is no more reason 
for excluding irregularities of passive nutrition, and of the 
supply of nutriment in these minute, microscopically invisible 
parts, than there is in the larger visible parts of the cells, 
tissues, and organs, consequently the descendants of a deter- 
minant can never all be exactly alike in size and capacity of 
assimilation, but they will oscillate in this respect to and fro 
about the maternal determinant as about their zero point, and 
will be partly greater, partly smaller, and partly of the same 
size as that. In these oscillations, now, the material for 
further selection is presented, and in the inevitable fluctu- 
ations of the nutrient supply, I see the reason why every 
step attained immediately becomes the zero point of new 
fluctuations, and consequently why the size of a part can 
be augmented or diminished by selection without limit, solely 
by the displacement of the zero point of variation as the 
result of selection.” 
The best illustration of this process of germinal selection 
is found, Weismann believes, in the case of the degeneration 
of organs. “For in most retrogressive processes active selec- 
tion in Darwin’s sense plays no part, and advocates of the 
Lamarckian principle, as above remarked, have rightly 
denied that active selection, that is, the selection of indi- 
viduals possessing the useless organ in its most reduced 
state, is sufficient to explain the process of degeneration. I, 
