But it may be that Spencer's assumption is the _simpler_ one? Quite the contrary, its simplicity is merely apparent. Whilst my theory needs for each modification only a modification of _one_ constitutional element of the germ, that is, of _one_ particle of the germinal substance, according to Spencer _every_ particle of that substance must change, for they are all supposed to be and to remain alike. But seeing that all hereditary differences, be they of individuals, races, {57} or species, must be contained in the germ, the obligation rests on these similar units, or rather the capacity is required of them, to produce in themselves a truly enormous number of differences. But this is possible only provided their composition is an exceedingly complex one, or only on the condition that in every one of them are contained as many alterable particles as according to my view there are contained determinants in the whole germ. _The differences that I put into the whole germ, Spencer and his followers are obliged to put into every single unit of the germinal substance._ My position on this point appears to me incontrovertible so long as it is certain that the single characters can vary hereditarily; for, if a thing can vary independently, that is, _of its own accord_, and _from the germ_, then that thing must be represented in the germ by some particle of the substance, _and be represented there in such wise that a change of the representative particle produces no other change in the organism developing from the germ than such as are connected with the part which depends on it_. I conceive that even on the assumption of my constitutional elements (_Anlagen_) the germ-plasm is complex enough, and that there is no need of increasing its complexity to a fabulous extent. Be that as it may, the person who fancies he can produce a complex organism from a _really_ simple germinal substance is mistaken: he has not yet thoroughly pondered the problem. The so-called "epigenetic" theory with its _similar_ germinal units is therefore naught else than an evolution-theory where the primary constitutional elements are reduced to the molecules and atoms--a view which in my judgment is inadmissible. A _real_ {58} epigenesis from absolutely _homogeneous_ and not merely _like_ units is not thinkable. All value has been denied my doctrine of determinants[19] on the ground that it only shifts the riddles of evolution to an invisible terrain where it is impossible for research to gain a foothold.