DEVELOPMENT, INHERITANCE, AND METABOLISM In bringing the foregoing discussion into more direct relation with the general theory of cell-action we may recall that the cell nucleus appears to us in two apparently different roles. On the one hand, it is a primary factor in morphological synthesis and hence in inheritance, on the other hand an organ of metabolism especially concerned with the constructive process. These two functions we may with Claude Bernard regard as but different phases of one process. The building of a definite cell-product, such as a muscle-fibre, a nerveprocess, a cilium, a pigment-granule, a zymogen-granule, is in the last analysis the result of a specific form of metabolic activity, as we may conclude from the fact that such products have not only a definite physical and morphological character, but also a definite chemical character. In its physiological aspect, therefore, inheritance is the recurrence, in successive generations, of like forms of metabolism ; and this is effected through the transmission from generation to generation of a specific substance or idioplasm which we have seen reason to identify with chromatin. This remains true however we may conceive the morphological nature of the idioplasm —whether as a microcosm of invisible germs or pangens, as conceived by De Vries, Weismann, and Hertwig, as a storehouse of specific ferments as Driesch suggests, or as complex molecular substance grouped in micelle as in Nageli's hypothesis. It is true, as Verworn insists, that the cytoplasm is essential to inheritance ; for without a specifically organized cytoplasm the nucleus is unable to set up specific forms of synthesis. This objection, which has already been considered from different points of view, both by De Vries and Driesch, disappears as soon as we regard the egg-cytoplasm as itself a product of the nuclear activity ; and it is just here that the general role of the nucleus in metabolism is of such vital importance to the theory of inheritance. If the nucleus be the formative centre of the cell, if nutritive substances be elaborated by or under the influence of the nucleus while they are built into the living fabric, then the specific character of the cytoplasm is determined by that of the nucleus, and the contradiction vanishes. In accepting this view we admit that the cytoplasm of the egg is, in a measure, the substratum of inheritance, but it is so only by virtue of its relation to the nucleus, which is, so to speak, the ultimate court of appeal. The nucleus cannot operate without a cytoplasmic field in which its peculiar powers may come into play ; but this field is created and moulded by itself. Both are necessary to development ; the nucleus alone suffices for the inheritance of specific possibilities of development.