394 1HE GERM-PLASM 



signifying 'enlargement/ If such an explanation were at- 

 tempted, we should be compelled to imagine that every cell in 

 the body was placed in communication with every germ-cell of 

 the ovary or spermarium by means of a large number of nerve- 

 tracks, and was capable of continually sending information to 

 the germ-cells of what was occurring in its own substance, and 

 of the manner in which it was influenced, and also of giving 

 instructions how each of the millions of units in the germ-plasm 

 should behave. I believe that it would be impossible to avoid 

 absurdities in explanations of this kind, and consider the whole 

 idea inadmissible. 



The second possible explanation appears to me to be less 

 acceptable at the present day tlian when it was put forward 

 by Darwin in the form of a hypothesis of pangenesis. And. as 

 already stated in earlier essays, I believe that the talented 

 author of this hypothesis of heredity did not look upon it as 

 a well-grounded assumption, but considered it merely as a 

 working hypothesis, only intended to lead to a better insight. 

 Meanwhile, many changes have been made, and we have 

 become acquainted with facts which compel us to reject the 

 idea of a ' circulation of gemmules," and I am surprised that 

 this has not hitherto been done. This hypothesis is rendered 

 inadmissible, not merely because we must imagine that the 

 gemmules are gh'e?i off, and then circulate through the body, 

 but principally on account of the implied addition of gemmules 

 — i.e., of p?'i>nary constituents — to the ger/n-plasni of the 

 germ-cells ! 



According to Darwin's idea, there must be a constant addition 

 of * primary constituents " or gemmules to the germ-plasm 

 already present in the germ-cells, unless, indeed, it is assumed 

 that the entire nuclear substance in the germ-cells is formed by 

 gemmules which migrate into them. Such an assumption is, 

 however, contradicted by the fact that the hereditary substance 

 of the germ-cells, which we obser^'e in the for )n of nuclear rods or 

 idants, receives 7io addition to its organised bodies, the primary 

 constitue?its. I have come to this conclusion, not from the fact 

 that we have never observed an addition of this kind, but from 

 the way in which the hereditary substance has been shown to 

 behave during its multiplication. We know that the cell contains 

 a most wonderful mechanism which apparently has the sole 

 function of distributing the idants quantitatively and qualitatively, 



