IV.] FOUNDATION OF A THEORY OF HEREDITY. 1 95 



particles than the nucleoplasm which only contains a single 

 modification, capable of determining the character of a single 

 kind of cell. The development of the nucleoplasm during 

 ontogeny may be to some extent compared to an army com- 

 posed of corps, which are made up of divisions, and these of 

 brigades, and so on. The whole army may be taken to repre- 

 sent the nucleoplasm of the germ-cell : the earliest cell-division 

 (as into the first cells of the ectoderm and endoderm) may be 

 represented by the separation of the two corps, similarly formed 

 but with different duties : and the following cell-divisions by 

 the successive detachment of divisions, brigades, regiments, 

 battalions, companies, etc. ; and as the groups become simpler 

 so does their sphere of action become limited. It must be ad- 

 mitted that this metaphor is imperfect in two respects, first, 

 because the quantity of the nucleoplasm is not diminished, but 

 only its complexity, and secondly, because the strength of an 

 army chiefly depends upon its numbers, not on the complexity 

 of its constitution. And we must also guard against the sup- 

 position that unequal nuclear division simply means a separation 

 of part of the molecular structure, like the detachment of a 

 regiment from a brigade. On the contrary, the molecular con- 

 stitution of the mother-nucleus is certainly changed during 

 division in such a way that one or both halves receive a new 

 structure which did not exist before their formation. 



My opinion as to the behaviour of the idioplasm during 

 ontogeny, not only differs from that of Nageli, in that the latter 

 maintains that the idioplasm only undergoes changes in its 

 ' conditions of tension and movement,' but also because he 

 imagines this substance to be composed of the preformed 

 germs of structures (' Anlagen '). Nageli's views are obviously 

 bound up with his theory of a continuous network of idioplasm 

 throughout the whole body ; perhaps he would have adopted 

 other conclusions had he been aware of the fact that the idio- 

 plasm must only be sought for in the nuclei. Nageli's views as 

 to ontogeny can be best seen in the following passages : ' As 

 soon as ontogenetic development begins, the groups of micellae 

 in the idioplasm which effect the first stage of development, 

 enter upon active growth : such activity causes a passive growth 

 of the other groups, and an increase in the whole idioplasm, 

 perhaps to many times its former bulk. But the intensities of 



2 



