206 THE CONTINUITY OF THE GERM-PLASM AS THE 



G. Jager l was the first to state that the body in the higher 

 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 explana- 

 tion. As I have previously mentioned in the introduction, Nuss- 

 baum also brought forward this hypothesis at a later period, and 

 also based it upon a continuity of the germ-cells. He assumed 

 that the fertilized egg 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 2 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 



1 Gustav Jager, ' Lehrbuch der Allgemeinen Zoologie,' Leipzig, 1878; II. 

 Abtheilung. Probably on account of the extravagant and superficial speculations 

 of the author, the valuable ideas contained in his book have been generally over- 

 looked. It is only lately that I have become aware of Jager's above-mentioned hy- 

 pothesis. 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 observations 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 ! 



[ 2 Facts of the same kind are also known in the Vascular Cryptogams, Muscineae , 

 Characeae, Florideae, etc. S. S.] 



