58 CHILDHOOD OF ANIMALS 



animal remains alive, ceased. Other naturalists have supposed 

 that the business of reproduction, and especially the rapid formation 

 and deposition of great quantities of eggs, throw a fatal strain on 

 the insect and that it dies of exhaustion. Metchnikoff has shown 

 that many insects appear to die from a kind of self-poisoning, or 

 from the attack of some microbial parasite, and if this be a usual 

 event, it is clear that the process of reproduction should be hurried 

 on as quickly as possible, to secure that it shall have taken place 

 before the insect dies. What at least is certain is an association 

 between the acceleration of reproduction and the shortening of the 

 adult life. When the next generation has been provided for, the 

 adults have accomplished their mission in life and are no longer 

 required. Whether they die from exhaustion, or because their 

 tissues have an inherently limited duration of life, or because they 

 are unable to resist the attacks of poisons from without or from 

 within, may some time be solved. To me it seems most probable 

 that the influence of natural selection has worked through speeding 

 up the process of reproduction, until that occurred so quickly that 

 it almost certainly would have taken place before the various 

 accidents from within and from without destroyed the adult. 

 Creatures subject to great destruction by other animals, creatures 

 that had little powers of resistance to microbes, or that were specially 

 liable to die because of the inherent delicacy of their constitutions, 

 would become extinct unless they reproduced as soon as possible. 

 Among a very large number of different animals there are wide 

 individual differences in the time when sexual maturity occurs. 

 Stock-breeders have taken advantage of this natural variability, 

 and have produced breeds which become mature at unusually early 

 ages when the object is to grow animals for the table as cheaply as 

 possible, or breeds that mature later when the object is to secure 

 special strength and stamina ; and it seems extremely probable 

 that similar changes have come about under natural conditions, 

 according to the needs of the particular species. The postponement 

 of reproduction lengthens the period of youth, and gives a greater 

 opportunity for education before the absorbing responsibilities of 

 adult life have been assumed. The acceleration of reproduction 

 secures that a species which has many enemies should leave abundant 

 progeny, although it may actually lead to a degeneration of the 

 structure and qualities of the adults. 



Among insects generally there is a kind of division of labour 

 between the larval and the adult stages. In the larval period the 



