36 The Selection Theory 
the struggle for existence, and they are therefore preserved by 
natural selection. Even the sterility itself in this case is not dis- 
advantageous, since the fertility of the true females has at the same 
time considerably increased. We may therefore regard the sterile 
forms of ants, which have gradually been adapted in several directions 
to varying functions, as a certain proof that selection really takes 
place in the germ-cells of the fathers and mothers of the workers, 
and that special complexes of primordia (ids) are present in the 
workers and in the males and females, and these complexes contain 
the primordia of the individual parts (determinants). But since 
all living entities vary, the determinants must also vary, now in a 
favourable, now in an unfavourable direction. If a female produces 
eges, which contain favourably varying determinants in the worker- 
ids, then these eggs will give rise to workers modified in the favourable 
direction, and if this happens with many females, the colony 
concerned will contain a better kind of worker than other colonies. 
I digress here in order to give an account of the intimate pro- 
cesses, which, according to my view, take place within the germ- 
plasm, and which I have called “germinal selection.” These processes 
are of importance since they form the roots of variation, which in 
its turn is the root of natural selection. I cannot here do more 
than give a brief outline of the theory in order to show how the 
Darwin-Wallace theory of selection has gained support from it. 
With others, I regard the minimal amount of substance which is 
contained within the nucleus of the germ-cells, in the form of rods, 
bands, or granules, as the germ-substance or germ-plasm, and I call 
the individual granules ids. There is always a multiplicity of such 
ids present in the nucleus, either occurring individually, or united in 
the form of rods or bands (chromosomes). Each id contains the 
primary constituents of a whole individual, so that several ids are 
concerned in the development of a new individual. 
In every being of complex structure thousands of primary con- 
stituents must go to make up a single id; these I call determinants, 
and I mean by this name very small individual particles, far below the 
limits of microscopic visibility, vital units which feed, grow, and 
multiply by division. These determinants control the parts of the 
developing embryo,—in what manner need not here concern us. The 
determinants differ among themselves, those of a muscle are differently 
constituted from those of a nerve-cell or a glandular cell, etc, and 
every determinant is in its turn made up of minute vital units, which 
I call biophors, or the bearers of life. According to my view, these 
determinants not only assimilate, like every other living unit, but they 
vary in the course of their growth, as every living unit does ; they 
may vary qualitatively if the elements of which they are composed 
