EX VIRIBUS VIVIMUS. 



of most complex factors, which do not permit us to 

 trace in the majority of organisms the operation of 

 the astronomical cause. The duration of life^ is 

 vastly influenced by varying conditions in various 

 organisms, but the prime factor in all cases is the 

 influence of changing day and night, of alternate 

 winter and summer, or wet and dry season.^ How 

 this influence is modified by the creation of cor- 

 respondences between organisms and their sur- 

 roundings, or how, in the words of the philosophy 

 of evolution, new factors have arisen in the pro- 

 gressive development of organisms by the law of 

 the survival of the fittest, is to be the subject of 

 enquiry in this essay. 



Although it is vain (with present knowledge) to 

 expect to gain a complete insight into those agree- 

 ments between beings and their environment, of 

 which the duration of life is one, yet certain facts 

 and considerations have been pointed out which go 



•■ The great importance which man attaches himself to long life, gives 

 the enquiry into longevity in aniiiials a greater importance than it deserves 

 as .% physiological or philosophical question. The varying intensity of 

 life in different species, and the average mortality of a species, are more 

 clearly influential quantities in nature than the possible length of life. 

 Time does not appear in the organic world as an easily recognisable 

 factor, for though in life as in levers what is lost in power is gained in 

 time, it is diflicult to distribute the amount of life of any given species 

 rightly between intensity and length. 



" In other words, astronomical cycles have furnished the unit for 

 organic cycles. The cyclical character has been as it were impressed 

 upon organic matter, by the great cycles of the universe. No further 

 implication is intended in the text: 



