21 CONTINUITY OF THE GERM-PLASM AS THE [IV. 



organisms is made up of two kinds of cells, viz., ontogenetic 

 and phyletic cells, and that the latter, the reproductive cells, 

 are not a product of the former (the body-cells), but that they 

 arise directly from the parent germ-cell. He assumed that the 

 ^ formation of germ- cells takes place at the earliest stage of 

 ' embryonic life, and he thus believed the connexion between 

 the germ-plasm of the parent and of the offspring had received 

 a satisfactory explanation. As I have previously mentioned 

 in the introduction, Nussbaum also brought forward this hypo- 

 thesis at a later period, and also based it upon a continuity of 

 the germ-cells. He assumed that the fertilized ^^g is divided 

 into the cells of the individual and into the cells which effect 

 the preservation of the species, and he supported this view 

 by referring to the few known cases of early separation of the 

 sexual cells. He even maintained this hypothesis when I had 

 proved in my investigations on Hydromedusae that the sexual 

 cells are not always separated from the somatic cells during 

 embryonic development, but often at a far later period. Not 

 only is the hypothesis of a direct connexion between the 

 germ-cells of the offspring and parent broken down by the 

 facts known in the Hydroids, and in the Phanerogams^ which 

 resemble them in this respect, but even the instances of early 

 separated germ-cells quoted by Jager and Nussbaum do not 

 as a matter of fact support their hypothesis. Among existing 

 organisms it is extremely rare for the germ-cells to arise 

 directly from the parent egg-cell (as in Diptera). If, however, 

 the germ-cells are separated only a few cell-generations later, 

 the postulated continuity breaks down ; for an embryonic cell, 

 of which the offspring are partly germ-cells and partly somatic 

 cells, cannot itself possess the nature of a germ-cell, and its 

 idioplasm cannot be identical with that of the parent germ-cell. 

 In order to prove this, it is only necessary to refer to the 

 arguments as to the ontogenetic stages of the idioplasm. In 



aware of Jager's above-mentioned hypothesis. M. Nussbaum seems to 

 have also arrived at the same conclusion quite independently of Jager. 

 The latter has not attempted to work out his hypothesis with any degree 

 of completeness. The above-mentioned obser\^ations are followed 

 immediately by quite valueless considerations, as, for instance, that the 

 ontogenetic and phyletic groups are in concentric ratio ! The author 

 might as well speak of a quadrangular or triangular ratio ! 



\} Facts of the same kind are also known in the Vascular Cryptogams, 

 Muscineae, Characeae, Florideae, etc.— S. S.] 



\ 



