328 THE EVOLUTION THEORY 



reproduction,' and try to probe more deeply into the meaning of its 

 establishment; in the meantime I must restrict myself to having 

 shown its significance in the union of the hereditary substances of 

 two individuals, and at the same time to controverting the theory 

 of the ' rejuvenating power ' of amphimixis. I use this expression in 

 its original sense, which indicates that every life is gradually wearing 

 itself away and would become extinct were it not fanned to flame 

 again by amphimixis — by an artifice of Nature, we may say. This 

 conception rests on the fact that the cells of the multicellular body 

 possess for the most part only a limited length of life, for they are 

 used up by the processes of life, and they break up ar/td <ii6, some 

 sooner, some later. As it is observed that all true somatic cells, 

 among higher animals at least, are subject to this law of mortality, 

 1 ;ut that the germ-cells are not, and that, furthermore, the germ-cells 

 only develop when they are fertilized, the cause of the potential 

 immortality of the germ-cells is believed to lie in amphimixis, and 

 a 'rejuvenating' power in fertilization, or, more generally, in amphi- 

 mixis, is inferred. Mystical as this sounds, and little as it agrees 

 with our otherwise mechanical conceptions of the economy of life, 

 it was until very recently a widespread view, although perhaps it is 

 now abandoned by many who formerly held it, and has been im- 

 perceptibly modified into a quite different conception, for which the 

 word ' rejuvenescence ' is retained, but with the altered meaning of a 

 mere ' strengthening of the metabolism ' or ' of the constitution.' By 

 many authors, indeed, the two meanings of the word are not clearly 

 kept apart. I shall return later to the modified meaning of the word 

 'rejuvenescence,' and shall keep in the meantime to the original 

 meaning of the word, which implies a renewal of life which would 

 otherwise die out. 



This meaning seemed to gain a firm hold, when, about fifteen years 

 ago, the French investigator Maupas published his remarkable obser- 

 vations on the conjugation of Infusorians. These seemed to show 

 that colonies of Infusorians which were artificially prevented from 

 conjugating gradually died out; not of course at once, but after 

 many, often several hundred, generations; ultimately a degeneration 

 of all the animals in such colonies set in, and ended only with their 

 utter extinction. Maupas himself interpreted this as a senile de- 

 generation which took place because conjugation had been prevented, 

 and he therefore regarded conjugation as a ' rajeunissement Icaryo- 

 fjaviique,' a rejuvenescence, and therefore a means of preventing the 

 ageing and final dying off" of the individuals— of obviating, in short, 

 the natural death to which in his opinion they would otherwise be 



