We have not yet considered one feature of all experiments in hybridisation, which indeed seems to be the most important of all for the theory of inheritance, if taken together with the fact of the pureness of the germs. The rule of Mendel always relates to one single character of the species or varieties concerned in hybridisation, and if it deals with more than one character, it regards every one of them separately; indeed, the rule holds for every one of them irrespective of the others. We cannot study here how this most important fact of the independence of the single characters of a species with regard to inheritance leads to the production of new races, by an abnormal mixture of those characters. We only take advantage of the fact theoretically, and in doing so, I believe, we can hardly escape the conclusion that the independence of the single characters in inheritance, taken together with the pureness of the germ-cells in the most simple form of hybrids, proves that there occurs in inheritance a sort of handing over of single and separate morphogenetic agents which relate to the single morphogenetic characters of the adult. We may use Bateson’s word “allelomorphs” for these agents, or units, as they may be called, thereby giving expression to the fact that the single and separate units, which are handed over in inheritance, correspond to each other in nearly related species without being the same. And so we have at least an inkling of what the material continuity of inheritance is to mean, though, of course, our “single and separate morphogenetic agents,” or “units” or “allelomorphs” are in themselves not much more than unknown somethings described by a word; but even then they are “somethings.” Besides the researches relating to the rule of Mendel and its exceptions, founded, that is, upon a study of the “second” generation of hybrids, there is another important line of research lately inaugurated by Herbst, which investigates the first generation in hybridisation. The hybrids themselves are studied with the special purpose of finding out whether the type of the single hybrid may change according to the conditions of its development, both outer and inner. The discoveries thus made may lead some day to a better understanding of the intimate nature of the “units” concerned in heredity, and perhaps to some knowledge of the arranging and ruling factor in morphogenesis also.