THE CYCLE OF LIFE 443 



animals, in which the dechne of hfe is marked by normal 

 senescence. (4) The fourth is that of many human beings, 

 not a few domesticated animals, e.g. horse, dog, cat, and 

 some semi-domesticated animals, notably bees, in which 

 the close of hfe is marked by distinctively pathological 

 senility. It seems certain that wild animals rarely exhibit 

 more than a shght senescence, while man often exhibits 

 a bathos of senihty. What is the reason of this ? 



The majority of wild animals seem to die a violent death, 

 before there is time for senescence, much less senihty. 

 The character of old age depends upon the nature of the 

 physiological bad debts, some of which are more unnatural 

 than others, much more unnatural in tamed than in wild 

 animals, much more unnatural in man than in animals. 

 Furthermore, civilized Man, sheltered from the extreme 

 physical forms of the struggle for existence, can hve for a 

 long time with a very defective hereditary constitution, 

 which may end in a period of very undesirable senihty. 

 Man is very deficient in the resting instinct, and seldom 

 takes much thought about resting habits. In many cases, 

 too, there has come about in human societies a system of 

 protective agencies which allow the weak to survive through 

 a period of prolonged senihty. We cannot, perhaps, do 

 otherwise ; but it is plain that to heighten the standard 

 of vitality is an ideal more justifiable biologically than 

 that of merely prolonging existence. For if old age be 

 then permitted, it is more likely to be without senihty. 

 Those whom the gods love die young. 



In Illustration 

 Freshwater Sponge. — Some of the simplest animals 

 or Protozoa have very complex hfe-histories, especially 



