Till within a few decades ago it was believed that in this process one individual devoured the other, but this can now no longer be maintained. If any one still seriously considers this possible, Schaudinn's observations would convince him of his error, for in _Trichosphærium_, a marine, many-nucleated Rhizopod, he observed, on the one hand, the union of two or more animals, i. e. plastogamy, and on the other hand, the swallowing and digesting of a smaller member of the species by a larger one--two processes which are absolutely different, for in the first case the cell-bodies of the two animals remain intact, while an animal that is eaten becomes surrounded by a food-vacuole, and is dissolved and digested within it. In the former case the vital units (biophors) of each animal obviously remain intact and capable of function; in the second, those of the over-mastered animal are at once dissolved and chemically broken up; as biophors, therefore, they cease to exist. Whether one or the other process takes place may perhaps depend on whether the two animals differ greatly in size, so that the smaller can be quite surrounded by the larger. In a former lecture I have emphatically expressed my dissent from the view which interprets amphimixis as a process of rejuvenation, meaning thereby a necessary renewal of life, and I need not go into this again in detail: for that the metabolism can continue through uncounted generations without being artificially stimulated--that is, in any other way than by nutrition--is proved by all those lowly organisms which exhibit neither plastogamy nor complete amphimixis, and also by the occurrence of purely parthenogenetic reproduction, &c. In what, then, can the advantage lie which the conjugating unicellular organisms derive from conjugation? Obviously not in that they impart to each other what each already possessed, but only in the communication of something special and individual, something that was peculiar to each, and becomes common to both. Haberlandt believed that the development of auxo-spores in Diatoms pointed towards the processes which form the deepest roots of amphimixis. As is well known, the hard and unyielding flinty shell of these lowly Algæ involves a diminution of the organism at every division, so that the Diatoms become smaller and smaller as they go on multiplying, and if that went on without limit they would come rapidly to extinction. But a corrective is supplied in the periodical occurrence of conjugation of two organisms which have already materially diminished in size, and this is followed by the growth of the two fused individuals to the original normal size of the species.