A full discussion of this question would be unsuitable in a work like this. We will therefore content ourselves with making three brief remarks: _a._ If the views presented in the early part of this chapter are true, then the Lamarckian factors must be true factors, _because there was a time when there were no others_. They were therefore necessary, at least to start the process, even if no longer necessary at present. _b._ But if these factors were ever operative, _they must be so still_, though possibly in a subordinate degree. A lower factor is not abolished, but only becomes subordinate to a higher when the latter is introduced. Thus it may well be that Lamarckian factors are comparatively feeble at the present time and among living species, especially of the higher animals, and yet not absent altogether. In the earliest stages of evolution there was a _complete identification of germ-cells and somatic cells_--of the individual with the species. In such cases, of course, any effect of the environment must be inherited and increased from generation to generation. But the differentiation of the germ and somatic cells was not all at once, nor is their sympathetic relation completely severed. It was a _gradual process_, and therefore the effect of the environment _on the germ-cells through the somatic cells_ continued, though in decreasing degree, and still continues. The differentiation in the higher animals is now so complete that germ-cells are probably not at all affected by changes in somatic cells, unless these changes are _long continued in the same direction, and are not antagonized by natural selection_. _c._ It is a general principle of evolution that the _law of the whole is repeated with modifications in the part_. This is a necessary consequence of the unity of Nature. We ought to expect, therefore, and do find, that the order of the use of the factors of evolution is the same in the evolution of the _organic kingdom_, in the evolution of _each species_, and in the evolution of _each individual_. In all these the physical factors are at first powerfully operative; these become subordinate to organic factors, and these, in their turn, to psychical and rational factors. Therefore, as the individual in its early stages--i. e., in embryo and infancy--is peculiarly plastic under the influence of the physical environment, and afterward becomes more and more independent of these; so a species when first formed is more plastic under the influences of Lamarckian factors, and afterward becomes more rigid to the same. And so also the organic kingdom was at first more plastic under Lamarckian factors, and has become less so in the present species, especially in the higher animals. The principal reason of this, as we have already seen, is the increasing differentiation of germ and somatic cells, and the removal of the former to the interior, where they are more and more protected from external influence.