180 THE CONTINUITY OP THE GERM-PLASM AS THE 



extent our opinions coincide. The nature of heredity is based upon 

 the transmission of nuclear substance with a specific molecular con- 

 stitution. This substance is the specific nucleoplasm of the germ- 

 cell, to which I have given the name of germ-plasm. 



O. Hertwig 1 has also come to the same conclusion : at an earlier 

 date he had looked upon the coalescence of nuclei as the most 

 essential feature in the process of fertilization. He now believes 

 that this former opinion has been confirmed by the recent dis- 

 coveries which have been shortly described above. 



Although I entirely agree with Hertwig, as far as the main 

 question is concerned, I cannot share his opinions when he identi- 

 fies Nageli's idioplasm with the nucleoplasm of the germ-cell. 

 Nageli's idioplasm certainly includes the germ-plasm, if I may 

 retain this expression for the sake of brevity. Nageli in forming 

 his hypothesis did indeed start with the germ-cells, but his idio- 

 plasm not only represents the nucleoplasm of the germ-cells, but 

 also that of all the other cells of the organism ; all these nucleo- 

 plasms taken together constitute Nageli's idioplasm. According 

 to Nageli, the idioplasm forms a network which extends through 

 the whole body, and represents the specific molecular basis which 

 determines its nature. Although this latter suggestion the 

 general part of his theory is certainly valid, and although it is 

 of great importance to have originated the idea of idioplasm in this 

 general sense, in contrast to the somato-plasm ('Nahrplasma'), it is 

 nevertheless true that we are not justified in retaining the details 

 of his theory. 



In the first place the idioplasm does not form a directly con- 

 tinuous network throughout the entire body ; and, secondly, the 

 whole organism is not penetrated by a single substance of homo- 

 geneous constitution, but each special kind of cell must contain 

 the specific idioplasm or nucleoplasm which determines its nature. 

 There are therefore in each organism a multitude of different 

 kinds of idioplasm. Thus we should be quite justified in generally 

 speaking of Nageli's idioplasm as nucleoplasm, and vice versa. 



It is perfectly certain that the idioplasm cannot form a con- 

 tinuous network through the whole organism, if it is seated in the 

 nucleus and not in the cell-body. Even if the bodies of cells are 



1 0. Hertwig, ' Das Problem der Befruchtung und der Isotropie des Eies.' Jena, 

 1885. 



