In conclusion it must be noticed, that Weismann now appears to have himself perceived the grave difficulties which lie against his antithesis between a hypothetical “germ-plasm” and a hypothetical “somato-plasm,” notwithstanding that the former becomes converted into the latter at each ontogeny. At any rate, he allows that Vines’ criticism upon this head is sound. But he is strongly of the opinion that, by means of a later emendation of his theory as originally published, he has succeeded in obviating these difficulties _in toto_. For my own part, as already several times observed in the text, I cannot in the least perceive that such is the case; and therefore I will quote _in extenso_ what he has said in answer to Professor Vines. It will be seen that his newer emendation of the theory consists in substituting for his original “somato-plasm” two substances, which are called respectively “somatic idio-plasm” and “cytoplasm.” And it is by means of this substitution that he thinks he has, in some way or another, overcome the contradiction involved in the doctrine (and, as it still seems to me, the essential doctrine of his whole theory of heredity) that “germ-plasm” becomes converted into “somato-plasm” during the course of every ontogeny. The following, at any rate, is his latest utterance upon the subject:— I believe that the objections which Professor Vines makes to my theory of the continuity of germ-plasma rest solely on an unintentional confusion of my ideas, as he compares the opinions expressed in the second essay with those of the later ones, with which they do not tally. I will endeavour to make this clear. In this second essay (1883) I contrasted the body (soma) with the germ-cells, and explained heredity by the hypothesis of a “Vererbungs-substanz” in the germ-cells (in fact the germ-plasma), which is transmitted without breach of continuity from one generation to the next. I was not then aware that this lay only in the nucleus of the ovum, and could therefore contrast the entire substance of the ovum with the substance of the body-cells, and term the latter “somato-plasm.” In Essay IV (1885) I had arrived, like Strasburger and O. Hertwig, at the conviction that the nuclear substance, the chromatin of the nuclear loops, was the carrier of heredity, and that the body of the cell was nutritive but not formative. Like the investigators just named, I transferred the conception of idio-plasm, which Nägeli had enunciated in essentially different terms, to the “Vererbungs-substanz” of the ovum-nucleus, and laid down that the nuclear chromatin was the idio-plasm not only of the ovum but of every cell, that it was the dominant cell-element which impressed its specific character upon the originally indifferent cell-mass. From then onwards, I no longer designated the cells of the body simply as “somato-plasm,” but distinguished, on the one hand, the idio-plasm or “Anlagen-plasma” of