§4 REMARKS ON CERTAIN [XL 



contains those of the ectoderm, and the other those of the 

 endoderm. The later stages of embryogeny depend on a con- 

 tinuance of such regular modifications of idioplasm. Each fresh 

 division sorts out fresh predispositions, previously mixed in 

 the nucleus of the mother-cell, until at length the full number 

 of embryonic cells have come into existence, each with an 

 idioplasm in its nucleus which stamps the specific histological 

 character upon the cell. 



I fail to understand why this idea presents such remarkable 

 difficulties to Professor Vines. In most species the separation 

 of the sexual cells takes place late in the embryogeny. Now in 

 order to maintain the continuity of germ-plasm from one gene- 

 ration to another, I have supposed that, at the first division of 

 the ovum, not all the germ-plasm (i.e. idioplasm of the first 

 ontogenetic stage) becomes changed into idioplasm of the 

 second stage, but that a minute portion of it persists unchanged 

 included in one or other of the daughter-cells, where it remains 

 inactive, intermingled with the nuclear idioplasm ; I have further 

 assumed that in this condition it is transmitted through a longer 

 or shorter series of cell-generations until at length it reaches 

 certain cells on which it impresses the characters of germ-cells, 

 and in these it resumes its activity. This view is not entirely 

 devoid of support ; for it is in some degree confirmed by actual 

 observations, especially by those on the remarkable wanderings 

 through which the germ-cells of Hydroids pass, after starting 

 from their original place of formation ^ 



But let us leave the consideration of the degree of probability 

 which my theory may possess, and consider only its logical 

 accuracy. Professor Vines says, ' The fate of the germ-plasm 

 of the fertilized ovum is, according to Professor Weismann, to 

 be converted in part into the somatoplasm (!) of the embryo, 

 and in part to be stored up in the germ-cells of the embryo. 

 This being so, how are we to conceive that the germ-plasm 

 of the ovum can impress upon the somatoplasm (!) of the de- 

 veloping embryo, the hereditary character of which it (the 

 germ- plasm) is the bearer ? This function cannot be discharged 

 by that portion of the germ-plasm of the ovum which has be- 



^ Weismann, ' Die Entstehung der Sexualzellen bei den Hydromedusen,' 

 Jena, 1883. 



