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 

 w orkers 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 

 eggs, 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 digi-ess 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 fi-om 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 gi-anules, as the germ-siibstance 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, gi'ow, and 

 multiply by division. Tliese 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 biopliors, 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 



