§ 80. Already, in the last two chapters, the law of hereditary transmission has been tacitly assumed; as, indeed, it unavoidably is in all such discussions. Understood in its entirety, the law is that each plant or animal, if it reproduces, gives origin to others like itself: the likeness consisting, not so much in the repetition of individual traits as in the assumption of the same general structure. This truth has been rendered so familiar by daily illustration as almost to have lost its significance. That wheat produces wheat--that existing oxen have descended from ancestral oxen--that every unfolding organism eventually takes the form of the class, order, genus, and species from which it sprang; is a fact which, by force of repetition, has acquired in our minds almost the aspect of a necessity. It is in this, however, that Heredity is principally displayed: the manifestations of it commonly referred to being quite subordinate. And, as thus understood, Heredity is universal. The various instances of heterogenesis lately contemplated seem, indeed, to be at variance with this assertion. But they are not really so. Though the recurrence of like forms is, in these instances, not direct but cyclical, still, the like forms do recur; and, when taken together, the group of forms produced during one of the cycles is as much like the groups produced in preceding cycles, as the single individual arising by homogenesis is like ancestral individuals. While, however, the general truth that organisms of a given type uniformly descend from organisms of the same type, is so well established by infinite illustrations as to have assumed the character of an axiom; it is not universally admitted that non-typical peculiarities are inherited. Many entertain a vague belief that the law of Heredity applies only to main characters of structure and not to details; or, at any rate, that though it applies to such details as constitute differences of species, it does not apply to smaller details. The circumstance that the tendency to repetition is in a slight degree qualified by the tendency to variation (which, as we shall hereafter see, is but an indirect result of the tendency to repetition), leads some to doubt whether Heredity is unlimited. A careful weighing of the evidence, however, and a due allowance for the influences by which the minuter manifestations of Heredity are obscured, may remove this scepticism.