DARWIN, NAEGELI AND DE VRIES 121 



Heredity is then easily accounted for, and is, in 

 fact, one of the phenomena Darwin explains best. 

 The transmission of acquired characters can be ex- 

 plained in the same way. Since at the very moment 

 when the organism undergoes a modification, the mod- 

 ified cells send to the sexual organs modified gem- 

 mules, the gemmules penetrating the cells of the new 

 organism must necessarily impart to it the modified 

 characters of the parent. 



If we grant these premises — the existence of gem- 

 mules and the properties Darwin ascribes to them — 

 this theory gives a simple and satisfactory explanation 

 of all the important biological phenomena, heredity, 

 variation, regeneration, sexual generation, etc. This 

 explanation appears so convincing that all modern 

 theories have borrowed the idea of representative par- 

 ticles without adding to it any essential detail. 



Can we, however, grant these premises? Unfor- 

 tunately we cannot. Even if we should admit the 

 existence of gemmules and of all their imaginary 

 properties, we would be confronted by a difficult prob- 

 lem : the mode of transmission of the gemmules from 

 one cell to another. How does the migration of gem- 

 mules take place, and what leads them, through innu- 

 merable series of cells in which they must not linger, 

 from one end of the organism to the other? This can 

 only be explained in two ways : The transmission can 

 be effected by the blood flux or by the nervous cur- 



