276 DEATH 



ductive cells in such way as to afford them the best 

 chance of completing their special duty, the per- 

 petuation of the species. 



The above considerations bring us to the final 

 point in Weismann's argument. If natural death 

 affects the somatic cells only, and is a character 

 acquired by them, it remains to inquire why such 

 natural death should occur, and what determines 

 the time of its occurrence. Weismann answers 

 these questions by saying that death occurs because 

 it is advantageous to the species that it should do 

 so ; and that the normal time for such death to 

 occur is the end of the reproductive period of the 

 individual. Both these points require further con- 

 sideration. With regard to the former it is of great 

 importance to distinguish clearly between what is for 

 the good of the individual on the one hand, and on 

 the other hand what is advantageous for the species. 

 A good illustration is afforded by the elaborate 

 provision which insects make for their offspring, 

 which they will never see. Certain wasps have 

 the habit of stinging the larvae of beetles in their 

 nerve centres in such manner as to paralyse their 

 victims without killing them. On the body of the 

 paralysed larva a single egg is laid by the wasp, 

 and then left to its fate. From the egg a grub is 

 hatched in due time, which at once begins to suck 

 the juices of the larva ; the victim supplying it with 

 food sufficient for the whole period of its develop- 

 ment. The grub changes to a pupa on the skin of 

 its victim, and passing through the winter in the 

 pupa state, emerges in the spring as a wasp with 



