174 CHARLES DARWIN. 



irregularity in number of gemmules, to their trans- 

 positions, and redevelopment when dormant ; and (2) 

 to their actual modification and the gradual replace- 

 ment by them of unaltered gemmules. 



Inheritance. — The non-transmission by heredity 

 of mutilations, even when repeated for many genera- 

 tions, as in docking the tails of certain domesticated 

 breeds, may be explained by the persistence of gem- 

 mules from still earlier generations. The cases of 

 inheritance when mutilations are followed by disease, 

 as in Brown-Sequard's experiments on guinea-pigs, 

 may be due to the gemmules being attracted to the 

 diseased part and there destroyed. 



The disappearance of a rudimentary part, together 

 with its occasional reappearance by reversion, is to be 

 understood by the existence of ancestral gemmules, 

 for which the corresponding cells have, except in the 

 cases of reversion, lost their affinity. When the 

 disappearance is final and complete, the gemmules 

 have probably perished altogether. 



" Most, or perhaps all, of the secondary characters 

 which appertain to one sex, lie dormant in the other 

 sex ; that is, gemmules capable of development into 

 the secondary male sexual characters are included 

 within the female ; and conversely female characters 

 in the male." This is seen in cases of castration or 

 when the sexual organs from any cause have become 

 functionless. The sex in which such changes are 

 brought about tends to develop the secondary sexual 

 characters of the other sex. The normal develop- 



