"We might almost reserve our belief that the structural [i. e. somatic] cells can react on the sexual elements at all, and we may be confident that at most they do so in a very faint degree; in other words, that acquired modifications are barely, if at all, _inherited_, in the correct sense of that word[27]." [27] _Theory of Heredity_ (Journ. Anthrop. Inst. 1875, p. 346). So far Mr. Galton; but for Weismann's further theory of evolution, &c., it is necessary to postulate the additional doctrine in question; and it makes a literally immeasurable difference to any theory of evolution whether or not we entertain this additional postulate. For no matter how faintly or how fitfully the substance of heredity may be modified by somatic tissues, the Lamarckian principles are hypothetically 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 any degree must always have been _directive_ of variation on the one hand, and _cumulative_ on the other. Thus, by merely laying this theory side by side with Weismann's we can perceive at a glance how a _pure_ theory of _heredity_ admits of being based on the postulate of Continuity alone, without cumbering itself by any further postulate as to this Continuity being _absolute_. And this, in my opinion is the truly scientific attitude of mind for us to adopt as preliminary to the following investigation. For the whole investigation will be concerned--and concerned only--with this question of Continuity as absolute, or as admitting of degrees. There is, without any question, abundant evidence to prove that the substance of heredity is at least partly continuous (Gemmules). It may be that there is also abundant evidence to prove this substance much more _largely_ continuous than Darwin supposed (Stirp); but be this as it may, it is certain that any such question as to the _degree_ of continuity differs, _toto caelo_, from that as to whether there can ever be any continuity at all.