Appendix I. 187 



just named, I transferred the conception of idio-plasm, which 

 Nageli 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 desig- 

 nated the cells of the body simply as " somato-plasm," but 

 distinguished, on the one hand, the idio-plasm or " Anlagen- 

 plasma" of the nucleus from the cell-body or " Cytoplasma," 

 and, on the other, the idio-plasm of the ovum-nucleus from that 

 of the somatic cell-nucleus ; I also for the future applied " germ- 

 plasm " to the nuclear idio-plasm of ovum and spermatozoon, 

 and " somatic idio-plasm " to that of the body cells (e.g , p. i£4). 

 The embryogenesis rests, according to my idea, on alterations 

 in the nuclear idio-plasm of the ovum, or "germ-plasm"; on 

 p. 186, et seq., is pictured the way in which the nuclear idio- 

 plasm is halved in the first cell-division, undergoing regular 

 alterations of its substance in such a way that neither half 

 contains all the hereditary tendencies, but the one daughter- 

 nucleus has those of the ectoblast, the other those of the ento- 

 blast ; the whole remaining embryogenesis rests on a con- 

 tinuation of this process of regular alterations of the idio-plasm. 

 Each fresh cell-division sorts out tendencies which were mixed 

 in the nucleus of the mother-cell, until the complete mass of 

 embryonic cells is formed, each with a nuclear idio-plasm which 

 stamps its specific histological character on the cell. 



I really do not understand how Professor Vines can find such 

 remarkable difficulties in this idea. The appearance of the 

 sexual cells generally occurs late in the embryogeny ; in order, 

 then, to preserve the continuity of germ-plasm from one 

 generation to the next, I propound the hypothesis that in 

 segmentation it is not all the germ-plasm (i. e., idio-plasm of the 

 first ontogenetic grade) which is transformed into the second 

 grade, but that a minute portion remains unaltered in one of 

 the daughter-cells, mingled with its nuclear idio-plasm, but in 

 an inactive state ; and that it traverses in this manner a longer 

 or shorter series of cells, till, reaching those cells on which it 

 stamps the character of germinal cells, it at last assumes the 



