Any theory of heredity which supposes the material of heredity to occupy a more or less separate “sphere” of its own, is not obliged further to suppose that this material has _always_ been thus isolated, or even that it is now _invariably_ so. There have been one or two such theories prior to Weismann’s, and they were founded on the well-known fact of congenital characters being at any rate _much more_ heritable than are acquired characters. But it has not been needful for these theories to assume that the “continuity” thus postulated has been _perpetually_ unbroken. Even if it has been frequently to some extent interrupted, all the facts of _heredity_ could be equally well comprised under such theories—and this even if it be supposed that acquired characters are but rarely, or never, transmitted to progeny. For, in as far as the continuity may have been interrupted, it does not follow that the acquired characters (body-changes), which by hypothesis caused the interruption, must be inherited by progeny exactly as they occurred in the parents. Or, in other words and adopting Weismann’s terminology, _so far as the facts of heredity are concerned_, there is no reason why germ-plasm should not frequently have had its hereditary qualities modified by some greater or less degree of commerce with somatic-tissues, and yet never have reproduced in progeny the identical acquired characters which caused the modification of germ-plasm in the parents: some other and totally different characters might with equal—or even more—likelihood have been the result, as we shall see more clearly a few pages further on. Why, then, does Weismann so insist upon this continuity of germ-plasm as _perpetual_ “since the origin of life”? It appears to me that his only reason for doing so is to provide a basis, not for his theory of heredity, but for his additional theory of evolution. It is of no consequence to the former that germ-plasm should be regarded as thus perpetual, while it is of high importance to the latter that the fundamental postulate of continuity should be supplemented by this further postulate of the continuity as thus perpetual. Similarly as regards the postulate of the stability of germ-plasm as absolute. It is enough for all the requirements of Weismann’s theory of heredity that the material basis of heredity should present a merely _high degree_ of stability, such as the facts of atavism, degeneration, &c. abundantly prove that it possesses. For his sequent theory of evolution, however, it is necessary to postulate this stability as _absolute_ “since the first origin of sexual reproduction.” Otherwise there would be no foundation for any of the distinctive doctrines which go to constitute this theory.