From the point of view of cells, I believe myself compelled to raise several objections to most important bases of Weismann's germplasm theory. For convenience of exposition these may be divided into two groups: Objections to the hypothesis of differentiating division; objections to Weismann's doctrine of determinants. I. OBJECTIONS TO THE HYPOTHESIS OF DIFFERENTIATING DIVISION. A corner-stone of Weismann's theory is his assumption of nuclear divisions which are differentiating. Proof of this fundamental assumption may be sought in vain in Weismann's writings. Instead of that, a series of abstract arguments are brought forward in favour of it. Thus on p. 31 (of the English translation) Weismann treats the chromatin in the nucleus of the fertilised egg as the substance which accomplishes inheritance, and he denotes all the nuclei of the organism arising from the nucleus of the egg by divisions as the chromatin-tree, and then goes on to ask whether or no the pieces of hereditary material that make up the chromatin-tree of an organism are like each other or different. 'It can easily be shown,' the answer runs, 'that the latter must be the case.' For 'the chromatin is in a condition to impress the specific character on the cell in the nucleus of which it is contained. As the thousands of cells which constitute an organism possess very different properties, the chromatin which controls them cannot be uniform; it must be different in each kind of cell.' Moreover, on p. 45 (of the English edition), 'The fact itself' (the capacity on the part of the idioplasm for regular and spontaneous change) 'is beyond doubt. When once it is established that the morphoplasm of each cell is controlled, and its character decided, by the idioplasm of the nucleus, the regular changes occurring in the egg-cell, and the products of its division in each embryogeny, must then be referred to the corresponding changes of the idioplasm.' Finally, on p. 205 (of the English edition), 'The cells of the segmenting ovum are completely dissimilar as regards their hereditary value, although they are all young and embryonic, and are not infrequently quite similar in appearance. It therefore seems to me to follow from this, as a logical necessity, that the hereditary substance of the egg-cell, which contains all the hereditary tendencies of the species, does not transmit them _in toto_ to the segmentation cells, but separates them into various combinations, and transmits them in groups to the cells. I have taken account of these facts in considering the regular distribution of the determinants of the germplasm, and the conversion of the latter into the idioplasm of the cells in the different stages of ontogeny.'