But we cannot see directly into the germ-plasm, and are therefore thrown back on the inductions we can make from the facts presented to us by the phenomena of visible living organisms. As yet the material for such inductions is scanty, because it has been got together haphazard, and not collected on a definite plan. I therefore refrain for the present from attempting any further elaboration of my germ-plasm theory. It is only when an abundance of observation material, collected according to a definite plan, lies at our disposal that anything more in regard to the intimate structure of the germ-plasm, or the mutual influences and relations of its determinants and its modification in the course of phylogeny can be deduced with any certainty. Meanwhile, we must content ourselves with having, through the hypothesis of determinants, made intelligible at least the one fundamental fact, how it is possible that in the course of the phylogeny single parts and single stages can be thrown out or interpolated, or even only caused to vary, without giving rise to variation in all the rest of the parts and stages of the animal. A theory of epigenesis cannot do this, for, if no representative particles were contained in the germ-plasm, then every variation of it would affect the whole course of development and every part of the organism, and variations of individual parts arising from the germ would be impossible.
Twofold import of amphimixis--It conditions the continual changing of individuality--Analogy from game of cards--The germ-plasm is at once variable and persistent--The two roots of individual variation: germinal selection and new combinations of the ids--'Harmonious' adaptation conditions amphimixis--Difference between adaptation and mere variation--Is a 'direct' use of amphimixis to be insisted upon?--Ceaseless intervention of personal selection in the lineage of the germ-plasm--Far-reaching effects of personal selection--Fixing of the arrangements for amphimixis in the course of generations of species--Increase of the constancy of a character with its duration--Characters in the same species variable in different degrees--The upper and under surfaces of Kallima--Wild plants brought under cultivation do not at first vary--Amphimixis very ancient, therefore very firmly established--Does amphimixis bring about equalization (Hatschek, Haycraft, Quetelet)?--Galton's frequency curves--Ammon's free scope for variations--De Vries' asymetrical curves of frequency.