Seeing, then, that Galton did not undertake to deny a possibly slight influence of somatic-tissues on the hereditary qualities of stirp, it follows that he did not have to proceed to those drastic modifications of the general theory of descent which Weismann has attempted. Stirp, like germ-plasm, is _continuous_; but, unlike germ-plasm, it is not _necessarily_ or _absolutely_ so. Again, stirp, like germ-plasm, is _stable_; yet, unlike germ-plasm, it is not _perpetually_ or _unalterably_ so. Hence we hear nothing from Galton about our having to explain the unlikeness of our children to ourselves by variations in our protozoan ancestors; nor do we meet with any of those other immense reaches of deductive speculation which, in my opinion, merely disfigure the republication of stirp under the name of germ-plasm. Now, I allude to these, the only important points of difference between stirp and germ-plasm, for the sake of drawing prominent attention to the fact that it makes a literally immeasurable difference whether we suppose the material basis of heredity to be _perpetually_ continuous and _unalterably_ stable, or whether we suppose that it is but _largely_ continuous and _highly_ stable. In the former case, all the far-reaching deductions which Weismann draws with reference to the general theory of descent—or apart from the more special problem of heredity—follow by way of logical consequence. In the latter case, there is no justification for any such deductions. For, no matter how faintly or how fitfully the hereditary qualities of the material in question may be modified by the somatic-tissues in which it resides, or by the external conditions of life to which it is exposed, these disturbances of its absolute stability, and these interruptions of its perpetual continuity, must cause more or less frequent changes on the part of its hereditary qualities—with the result that specific or other modifications of organic types need not have been solely due to the varying admixture of such material in sexual unions on the one hand, or to the unassisted power of natural selection on the other. Numberless additional causes of individual variation are admitted, while the Lamarckian principles are still allowed some degree of play. And although this is a lower degree than Darwin supposed, their influence in determining the course of organic evolution may still have been enormous; seeing that their action, in whatever measure it may be supposed to obtain, must always have been _cumulative_ on the one hand, and _directive_ of variations in adaptive lines on the other. Or, as Galton himself observes, in the passage already quoted, “if they exist, _in however faint a degree_, a complete theory of heredity must account for them.” He saw, indeed, that a most inviting _logical_ system could be framed by denying that they can ever exist in any degree—or, in other words, by supposing that stirp was _exactly_ the same as what was