122 THE THEORIES OF EVOLUTION 



rent. But Darwin does not admit the first explana- 

 tion and we know that the nervous current does not 

 carry particles of matter. 



There is another argument against it. Even sup- 

 posing that there is some mode of circulation yet un- 

 known to us, it remains to be shown how the gemmules 

 are steered towards certain cells. Darwin supposes 

 that before the arrival of the gemmules the cells are 

 all alike. How then can they exert a varying power 

 of attraction? On the other hand if the gemmules 

 themselves are endowed with a power of selection, why 

 should they select one cell in preference to another 

 identical cell? We must then suppose that there ex- 

 ists between cells very subtle differences which make 

 them favour certain gemmules. But how do we ac- 

 count for those differences? Not through the gem- 

 mules which have not reached them yet. And if any 

 other factor can produce those differences, it may as 

 well produce any other histological difference and we 

 can dispense with the gemmules. 



This is the weak point of the system and, in this re- 

 spect, it is frankly inferior to some of the later the- 

 ories. These theories do not deserve much credit for 

 their superiority, as they only improved upon an idea 

 which originated with Darwin. Many other theories 

 which we will not mention here are based on the prin- 

 ciple of cell-representation through special particles. 

 All of them are but slight modifications of Darwin's 



