It will be remembered that the primary or fundamental difference just alluded to is, that while the theory of germ-plasm postulates an _absolute_ continuity, the theory of stirp postulates but a _partial_ continuity, of the substance of heredity. Hence, according to Weismann’s view, we must go back to the unicellular organisms for the origin of this substance in the multicellular; and we must regard use-inheritance as physiologically impossible. On the other hand, according to Galton’s view, there is no necessity for us to do either of these things. The origin of stirp is to be found in the somatic tissues of the multicellular organisms themselves. Nevertheless, this theory differs greatly from pangenesis, in that the former supposes the origin of hereditary substance to be mainly given in the _phylogeny_ of any group of multicellular organisms, while the latter supposes it to be given mainly in each _ontogeny_, Galton’s theory is, that in each ontogeny only a small part of the stirp derived from parents is consumed in making the new organism—the larger part being handed over in trust for passing on to the next generation, in the same way as Weismann supposes to be the case with germ-plasm. Darwin’s theory, on the other hand, does not entertain any such notion of “continuity” in the substance of heredity from germ-cell to germ-cell of parent and offspring; it supposes that in each successive generation the germ-cells are _wholly_ supplied with their germinal material from somatic-cells of each individual organism. Or, adopting our previous terminology, the three theories may be ranked thus. The particulate elements of heredity all proceed centripetally from somatic-cells to germ-cells (gemmules): the inheritance of acquired characters is therefore habitual. These particulate elements proceed for the most part, though not exclusively, from germ-cells to somatic-cells (stirp): the inheritance of acquired characters is therefore but occasional. The elements in question proceed exclusively in the centrifugal direction last mentioned (germ-plasm): the inheritance of acquired characters is therefore impossible[43]. Such being the fundamental points of difference between these three theories of heredity, we have now to consider more particularly those which obtain between Galton’s and Weismann’s.