Following out this chain of ideas, Weismann attributes only to those cells which contain unaltered germplasm the power of giving rise to complete new individuals, while cells with histogenous nuclearplasm, whether these be embryonal cells or cells of the ectoderm or of the endoderm, he regards as having lost this capacity, because nuclearplasm of a simpler molecular structure cannot retransform itself into that with the more complicated structure. The further conclusion is necessary that a part of the nuclearplasm of the original nucleus of the fertilised egg-cell must remain unaltered throughout the various nuclear divisions, although it may be mingled with the nuclearplasms of certain series of cells. For these reasons, ova and spermatozoa can arise only when the germplasm which has been handed on from the original nucleus to certain cells is able to overcome the histogenous plasm of these cells. In this respect Weismann has amended his original proposition that the germ-cells were immortal, like unicellular organisms. In a strict and literal interpretation such a proposition would be incorrect, for the germ-cells are immortal only so far as they contain the germplasm, the immortal part of the organism. In its further elaboration Weismann's conception was influenced considerably by publications of Naegeli, De Vries, and Wiesner. These dealt with the composition of the hereditary material, and they contained new hypotheses concerning the primary structure of the cell-body. Weismann avowedly accepted the suggestion of De Vries, who had rehabilitated and modernized Darwin's doctrine of pangenesis, according to which gemmules, small particles endowed with the power of division, were the material bearers of hereditary characters. From these different sources Weismann has now worked out, in minutest detail, a theory to which he considers his former writings but as the preface; none the less, he has taken from his own writings the most essential and characteristic sequences of idea, in a fashion but slightly modified. Let me give the most important parts of his conception. The substance which is the bearer of the hereditary character of a species (the idioplasm of Naegeli) lies not in the general protoplasm of the ovum and spermatozoon, but in their nuclear matter (hypothesis of Hertwig and Strasburger). Weismann calls this the germplasm, so altering the previous connotation of the word. The germplasm of every species has an extremely complicated, stable architecture, an architecture that has been elaborated gradually in the course of past time. In this he distinguishes simple and complex component parts, the biophores, determinants, ids, and idants.