262 



organism dies by reason of the impossibility of any further growth 

 of the body. 



The reproductive cells are, then, the essential factors for the 

 continuance of the species, the somatic for the growth of the 

 individual. 



Now, it is evident, from the point of view of the species in 

 contradistinction to that of the individual, that a change from 

 the asexual to the sexual method of reproduction must carry with 

 it a distinct advantage, for, it must be remembered that the indi- 

 vidual exists for the good of the species. The advantage which 

 death possesses for the species appears on consideration of the 

 consequences which would ensue if these complex organisms were 

 endowed with immortality, for in such a case all those members 

 of a species which multiplied by sexual methods would, in the 

 course of time, come to be composed of broken down and decrepid 

 individuals, resulting from the inevitable disease and accidents 

 of life, and they would consequently be less well adapted for 

 their p]ace in nature than younger, healthier, and less-damaged 

 forms. 



The doom of death, then, appears to have been brought about 

 by natural selection, inasmuch as it is for the benefit of those 

 species which propagate themselves sexually, that the individual 

 composing them should not live longer than is necessary for the 

 purpose of giving origin to the next generation, and fairly 

 launching its members on their own career of struggle for 

 existence. 



Our position, therefore, stands thus at present : — Protoplasm 

 was originally immortal, and unicellular organisms still preserve 

 this attribute of immortality, but in the case of the multicellular 

 organisms which propagate sexually, natural selection has reduced 

 the term of life within the narrowest limits which are compatible 

 with the performance of the sexual act and the subsequent rear- 

 ing of the progeny up to the period at which they are capable of 

 taking care of themselves. 



The reproductive elements of their bodies alone have reserved 

 the attribute of immortality, as the means whereby a continuous 

 stream of life has been maintained from the time of its first 

 appearance until now. 



Wliy, then, should sexual reproduction, which carries with it 

 the doom of death, have become the universal law for all the 

 higher organisms ? Looking at its universality, it must be as- 

 sumed to play an all-important role in the scheme of organic life. 

 What is the role ? Briefly, according to Weismann, its object is 

 to furnish congenital variations to the ever ready and ever active 

 agency of natural selection, from which the most favourably 

 endowed examples of the species may be preserved, and their 



