294 BIOLOGY. [Book hi. 



it. In the Hgher vertebrates tMs decline of nutrition is im- 

 mediately attended by slackening of the pulse and of the 

 respiration. The animal offers less resistance to low tempera- 

 tures, often succumbs to them. 



During youth, assimilation prevails over disassimilation. In 

 old age the case is reversed. The tables published by Quetelet 

 show that the weight of the body diminishes from the fiftieth 

 year in man, and the sixtieth in woman. At ninety years this 

 weight is reduced in the former from 136 to 123 lbs., in the 

 latter from 120 to 103 and a half. 



The average duration of life varies, in the two organic king- 

 doms, with the species. 



In general, the lower organisms live a shorter time than the 

 higher organisms. Less richly endowed with organs and ap- 

 paratus, less differentiated, they harmonise less readily with the 

 feterior medium and its variations. At the longest, mushrooms 

 only live a few days. The infusoria sometimes complete the 

 cycle of their life in a few hours, and most of the invertebrated 

 animals have only a short existence. 



In general, life is short in proportion to the rapidity of growth 

 and of embryonary evolution. Aptitude for generation being in 

 some degree a sign of the full development of the organised 

 being, it is natural that its tardy appearance should be connected 

 with greater longevity. In fact, this is the case with most of 

 the vertebrated animals. In many invertebrated animals the 

 appearance of the generative functions is, on the contrary, the 

 forerunner of death. Numbers of insects die immediately after 

 having procreated. The male butterflies die even sometimes in 

 accomplishing the act of generation. The ephemerides live one 

 or two years in the state of larvse, and only a few hom-s as 

 perfect insects. 



In plants, fructification is also a supreme act, presaging a 

 complete and speedy death in herbaceous plants, a partial death 

 in the perennial vegetals. The celebrated saying of Proudhon, 

 " Love is death," is then in this case an exact expression of the 



