VIII A THEORY OF HEREDITY 279 



spring through the female parent without being mani- 

 fest in her ; and yet again the appearance at a particu- 

 lar period of life of characters inherited and remaining 

 latent in the young organism. According to the 

 hypothesis of pangenesis, " every unit or cell of the 

 body throws off gemmules or undeveloped atoms, 

 which are transmitted to the offspring of both sexes 

 and are multiplied by self-division. They may remain 

 undeveloped during the early years of life or during 

 successive generations ; their development into units 

 or cells, like those from which they were derived, 

 depending on their affinity for, and union with, other 

 units or cells previously developed in the due order of 

 growth.^' 



In an essay ("Comparative Longevity," Macmillan, 

 1870, p. 32) published six years ago, I briefly sug- 

 gested the possibility of combining Mr. Herbert 

 Spencer's and Mr. Darwin's hypotheses thus : " The 

 persistence of the same material gemmule and the 

 vast increase in the number of gemmules, and conse- 

 quently of material bulk,^ make a material theory 

 difficult. Modified force -centres, becoming further 

 modified in each generation, such as Mr. Spencer's 

 physiological units, might be made to fit in with Mr. 

 Darwin's hypothesis in other respects." In fact, in 

 place of the theory of emission from the constituent 

 cells of an organism of material gemmules which cir- 

 culate through the system and affect every living cell, 



1 On tills subject see Mr. Sorby's recent Presidential Address to the 

 Royal Microscopical Society, in the Quarterly Journal of Microscopical 



Science, April 1876. 



