The Begin n ing and End of Life 391 



each kind of animal has come to take place naturally just at 

 that time which is most beneficial to its species, and has so 

 been fixed for each by the operation of natural selection. 

 He argues that once the period of reproduction is finally 

 over, any further survival of parental organisms must be 

 prejudicial to the race, unless by their care of the young, or 

 some other benefit to the community, they more than com- 

 pensate for the loss of nourishment their survival occasions 

 to the still reproductive members of the species. The Pro- 

 fessor brings forward a great number of interesting facts with 

 regard to the vitality of different groups of animals, and the 

 facts brought forward by him of course tend on the whole to 

 support his hypothesis. But the duration of life differs 

 greatly in different creatures, even belonging to the same 

 natural group. 



As a rule, birds live long, and a white-headed vulture has 

 lived for one hundred and eighteen years in captivity. This 

 prolongation of bird-life Professor Weismann considers to be 

 due to the very large proportion of eggs destroyed by enemies 

 of so many different kinds, a circumstance which demands 

 a greater production of young by way of compensation. 

 Beasts, the immature progeny of which are sheltered within 

 the maternal organism, lose much less, and consequently 

 may produce less also, without risk to the permanence of the 

 species. Most insects are short-lived in the final or imago 

 stage of their existence. The Fphemeridce, the female 

 moths, Solenobia, and the male of Psyche calcella, do not 

 live even one entire day in that condition. On the other 

 hand. Sir John Lubbock has kept a queen-ant alive for 

 nearly fifteen years, and a beetle (Buprestis splendens) has 

 been known to live over thirty years. A very lowly 

 organism (the sea-anemone. Actinia Tnesembryanthemumi) 

 has even been found capable of living for no less than sixty- 

 six years. 



