170 CHARLES DARWIN. 



collected in bud or germ-cell are essentially similar ; 

 and were it not for the special advantages of sexual 

 reproduction (increased vigour and more marked vari- 

 ation of offspring), we can well believe that it would 

 have been much less general. The formation of graft- 

 hybrids, and the action of the male element on the 

 mother and on future offspring, become intelligible. 

 The antagonism between growth and sexual repro- 

 duction in animals, and between increase by buds, 

 etc., and seeds in plants, can be understood by the 

 use of gemmules in one direction preventing their 

 simultaneous use in another. 



The regrowth of an amputated part, as in the 

 salamander or snail, is explained by the presence and 

 development of gemmules previously thrown off from 

 the part. The difficulty that a limb is produced of 

 the same age as that which was lost, and not a larval 

 limb, and that the cells with which the gemmules 

 must unite at first are not those w^hich precede them 

 in the course of growth, but mature cells, is met by 

 the consideration that this power is a special one 

 adapted to meet special dangers to certain parts of 

 certain animals, and that it is therefore probable that 

 appropriate provision has been made by natural 

 selection : it may be in the form of " a stock of 

 nascent cells or of partially developed gemmules." 

 The existence of these latter in buds, and their 

 absence from sexual cells, may account for bud 

 development being the more direct and brief of the 

 two. The much greater tendency to repair lost parts 



