284 THE SIGNIFICANCE OF SEXUAL REPRODUCTION 



present, that factor which, in my opinion, is of the utmost import- 

 ance in conjugation, the fusion of two hereditary tendencies. If 

 rejuvenescence possesses any significance at all, it must be this, 

 that by its means a force, which did not previously exist in the 

 conjugating individuals, is called into activity. Such a force 

 would, however, owe its existence to latent energy stored up in 

 each single animal during the period of asexual reproduction, and 

 such latent forces would necessarily be of different natures, and of 

 such a constitution that their union at the moment of conjugation 

 would give rise to the active force of reproduction. 



The process might perhaps be compared to the flight of two 

 rockets, which by the combustion of some explosive substance (such 

 as nitro-glycerine) stored up within themselves are impelled in 

 such a direction that they would meet at the end of their course, 

 when all the nitro-glycerine had been completely exhausted. The 

 movement would then come to an end, unless the explosive material 

 could have been meanwhile renewed. Now suppose that such a 

 renewal were achieved by the formation of nitric acid in one of the 

 rockets and glycerine in the other, so that when they came into 

 contact nitro-glycerine would be formed afresh equal in quantity and 

 in distribution on both the rockets to that which was originally 

 present. In this way the movement would be renewed again and 

 again with the same velocity, and might continue for ever. 



Rejuvenescence can be rendered intelligible in theory by some 

 such metaphor, but considerable difficulties are encountered in 

 the rigid application of the metaphor to the facts of the case. 

 In the first place, how is it possible that the motive force can be 

 exhausted by continual division, while one of its components is 

 being formed afresh in the same body and during the same time ? 

 When thoroughly examined the loss of the power of division is 

 seen to follow from the loss of the powers of assimilation, nutrition, 

 and growth. How is it possible that such a power can be 

 weakened and finally entirely lost while one of its components 

 is accumulated? 



I believe that, instead of accepting such daring assumptions, it 

 is better to be satisfied with the simple conception of living 

 matter possessing as attributes the powers of unlimited assimilation 

 and capacity for reproduction. With such a theory the mere form 

 of reproduction, whether sexual or asexual, will have no influence 



