We thus reach what is perhaps a not wholly unsatisfactory conception of amphimixis, in so far at least that we do not require to assume that there has been a fundamental change in its significance between its expression in the lowest organisms and in the higher and even highest forms. Everywhere it is the same advantage: an increase in the power of adaptation; but it sometimes finds expression directly in the product of conjugation, sometimes only indirectly, sooner or later, among the descendants of the product. How far below the Myxomycetes pure plastogamy reaches we do not know; whether it also occurs among non-nucleated organisms (Haeckel's Monera) we cannot tell from experience, since these assumed organisms have not yet been observed with certainty. Perhaps they all lie below the limits of visibility, and then we could never do more than _suppose_ that plastogamic processes occur among them. Logically and purely theoretically we may _suppose_ that amphimixis occurred first between the plasmic bodies of non-nucleated Monera, then between the cell-bodies of true cells, and finally between the nuclei of cells. Let us hold fast to what we have found to be probable, namely, that the fusion of individually different simple organisms must or may bring about a direct advantage--a stimulation of the metabolism, and at the same time an improvement of the constitution in different directions, and let us go on to the consideration of cell-fusion combined with nuclear fusion, or complete amphimixis. In this something is added which we can recognize as an important advantage, namely, the combination of two hereditary substances, and thus the union of two variation-complexes which, according to our view, is necessary if transformation of species is to take place. In mere plastogamy such a union of two hereditary masses could only take place in Monera, not in nucleated organisms. If then there are really unicellular organisms which exhibit plastogamy without karyogamy (certain Foraminifera), we have a further proof that these processes of plasmic fusion imply direct advantage, which is distinct from the indirect advantage lying in the mingling of two different hereditary contributions, since in these cases of plastogamy there is no demonstrable mingling of hereditary bodies, no karyogamy.