FOUNDATION OF A THEORY OF HEREDITY. 191 



all be contained in the minute quantity of germ-plasm which is 

 possessed by the nucleus of a germ-cell ; not indeed as the pre- 

 formed germs of structure (the gemmules of pangenesis), but as 

 variations in its molecular constitution ; if this be impossible, 

 such characters could not be inherited. Nageli has shown in his 

 work, which is so rich in suggestive ideas, that even in so minute 

 a space as the thousandth of a cubic millimetre, such an enormous 

 number (400,000,000) of micellae may be present, that the 

 most diverse and complicated arrangements become possible. It 

 therefore follows that the molecular structure of the germ-plasm in 

 the fferm-cells of an individual must be distinguished from that 



o " 



of another individual by certain differences, although these may 

 be but small ; and it also follows that the germ-plasm of any 

 species must differ from that of all other species. 



These considerations lead us to conclude that the molecular 

 structure of the germ-plasm in all higher animals must be 

 excessively complex, and, at the same time, that this complexity 

 must gradually diminish during ontogeny as the structures still to 

 be formed from any cell, and therefore represented in the mole- 

 cular, constitution of its nucleoplasm, become less in number. I do 

 not mean to imply that the nucleoplasm contains preformed struc- 

 tures which are gradually reduced in number as they are given off 

 in various directions during the building-up of organs : I mean 

 that the complexity of the molecular structure decreases as the po- 

 tentiality for further development also decreases, such potentiality 

 being represented in the molecular structure of the nucleus. The 

 nucleoplasm, which in the grouping of its particles contains po- 

 tentially a hundred different modifications of this substance, must 

 possess far more numerous kinds and far more complex arrange- 

 ments of such particles than the nueleoplasm which only con- 

 tains 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 

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

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

 present 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 



