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194 CONTINUITY OF THE GERM-PIASM AS THE [IV. 



detail in the whole organism must be represented in the germ- 

 plasm by its own special and peculiar arrangement of the 

 groups of molecules (the micellae of Nageli), and that the 

 germ-plasm not only contains the whole of the quantitative and 

 qualitative characters of the species, but also all individual 

 variations as far as these are hereditary : for example the 

 small depression in the centre of the chin noticed in some 

 families. The physical causes of all apparently unimportant 

 hereditary habits or structures, of hereditary talents, and other 

 mental peculiarities, must all be contained in the minute quantity 

 of germ-plasm which is possessed by the nucleus of a germ- 

 cell ;— not indeed as the preformed 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 

 germ-cells of an individual must be distinguished from that 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 ex- 

 \ cessively 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 molecular constitution of its nucleoplasm, become less in 

 number. I do not mean to imply that the nucleoplasm contains 

 preformed structures 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 potentiality for further development 

 also decreases, such potentiality being represented in the mole- 

 cular structure of the nucleus. The nucleoplasm, which in the 

 grouping of its particles contains potentially a hundred different 

 modifications of this substance, must possess far more nu- 

 merous kinds and far more complex arrangements of such 



