6 ESSAYS SCIENTIFIC AND PHILOSOPHICAL. 



" The mortality of the somatic cells," says Professor 

 Weismann, " arose with the first differentiation of the 

 originally homogeneous cells of the polyplastids into the 

 dissimilar cells of the heteroplastids. And this is the first 

 beginning of natural death." 



At first, while the immortal reproductive cells 

 far outnumbered the perishable somatic cells, the 

 death of the latter would be hardly noticeable. 

 The organism, as a whole, would seem to survive, 

 though a part of it perished. But when, in the 

 individual, the perishable somatic cells came to 

 outnumber the reproductive cells, death would 

 emerge into prominence. For that which lived 

 would be relatively small and unimportant com- 

 pared with that which died. And when, more- 

 over, the potentially immortal germ cells, owing to 

 the death of the somatic cells, lacked the conditions 

 under which they might build up a new body, they 

 would also die, and so the natural death of the 

 somatic cells would become incidentally the cause 

 of death in the germ cells. For instance, if a plant 

 or insect dies before all the reproductive cells have 

 matured, these remaining cells are killed by the 

 death of the soma. And thus the mortal secures 

 an accidental triumph over that which in its own 

 nature was potentially immortal. 



If we ask Why did the mortal thus triumph 

 over the immortal ? the answer is that it must 

 have been for the good of the species. But this at 

 once suggests the further question, 



