rpE FORMATION OF GERM-CELLS 1 99 



A few years later, Galton changed his opinion and adopted 

 Darwin's theory of pangenesis, which he modified considerably, 

 and only used ' as a supplementary and subordinate part of a 

 complete theory of heredity.* This theory has already been 

 discussed in the Historical Introduction to this book. The 

 • gemmules ' which are contained in the fertilised ovum together 

 constitute the ' stirp ' or stock, which by means of the egg-cell 

 gives rise to a new individual. Each 'sort of gemmule ' is repre- 

 sented by a number of gemmules which differ somewhat from and 

 compete with one another ; and since the successful ones in the 

 competition for taking part in the construction of the body form 

 the various parts of the body and are therefore contained in 

 them, the rest remain unused, thus constituting the * residual 

 germs.' These, then, are * the parents of the sexual elements and 

 buds.' The * dominant ' gemmules may also take a part, though 

 only a slight one, in the formation of the germ-cells, 'as they 

 are the least fertile in the production of gemmules.' The germ- 

 cells are therefore mostly formed from gemmules which have 

 remained latent, and this accounts for the fact that the offspring 

 usually do not exhibit the most marked peculiarities of the 

 parent. As this hypothesis only accounts for the dissimilarity 

 between parent and child, so far as it exists, and not for the far 

 commoner resemblance between them, Galton assumes that the 

 parts of the body can also give off gemmules which become dis- 

 tributed and extend beyond the boundaries of the cells in which 

 they arose, and so may even penetrate into the sexual elements. 

 He thus substitutes the idea of a locally restricted distribution of 

 the gemmules for Darwin's view of their • free circulation.' If we 

 attempt to make this somewhat vague and unrealistic idea rather 

 more comprehensible, by considering the • residue of the stirp ' 

 as equivalent to the • unalterable " reserve germ-plasm, Galton's 

 hypothesis will be found to bear some resemblance to the theory 

 of the continuity of the germ-plasm. But there is still a 

 fundamental difference between them, for Galton's idea is only 

 conceivable on the presupposition of the occurrence of sexual 

 reproduction, while the theory of the continuity of the germ- 

 plasm is entirely independent of any assumption as to whether 

 each primary constituent is present in the germ singly or in 

 numbers. According to my idea, the active and the reserve 

 germ-plasm contain precisely similar primary constituents, gem- 

 mules, or determinants ; and on this the resemblance of a child 



