AN- ESS A Y ON LONGEVITY. 3 1 



and when supplied with proper nutriinent multiply by 

 self-division, subsequently becoming developed into 

 cells like those from which they were derived. They 

 are supposed to be transmitted from the parents to 

 the offspring, and are generally developed in the 

 generation which immediately succeeds, but are often 

 transmitted in a dormant state during many genera- 

 tions, and are, then developed. Their development 

 is supposed to depend on their union with other 

 partially developeid cells or gemmules which precede 

 them in the regular course of growth.' ' Gemmules 

 are supposed to be thrown off by every cell or unit, 

 not only during the adult state, but during all the 

 stages of development' (Darwin, loc. cit. vol. ii. 



P- 374.) 



We may use this theory to explain the hereditary 

 character of senility. The gemmules, ' when supplied 

 with proper nutriment, multiply.' As long as there 

 is nutriment for them they will continue to be pro- 

 duced, but when the superabundance of nutriment 

 ceases, which, as we shall see, is soon after growth is 

 quite completed, their production ceases ; they are 

 thus limited in number, and, being called upon in 

 repair and reproduction, are gradually exhausted. 

 But it is not necessary to have recourse to the 

 pangenetic gemmules, which are only considered 

 by Mr. Darwin as provisional hypotheses.' The 



■ Mr. Darwin does not appear to connect the gemmules with 

 ordinary repair (i. e. of waste, not injury), which it would be more satis- 



