462 LIFE : OUTLINES OF GENERAL BIOLOGY 



of development also: the long obsessive insistence on lion or tiger 

 in terms of teeth and claws, and the corresponding low estimate 

 of the apx^s and monkeys, notwithstanding. 



REPRODUCTION AND DEATH.— WhUe reproduction is con- 

 cerned with the beginning of new lives, it not infrequently involves 

 the ending of the life of the parent. In many organisms, repro- 

 duction is the beginning of death. The sur\'ival of annual plants 

 to become biennials and perennials is thus one of the most notable 

 advances of plant life. In some relatively simple animals, such 

 as certain Annelid worms, the parent, especially the mother, may 

 rupture and die in liberating the reproductive elements. The case 

 of the Palolo-worms, Eunice viridis and others, is of special interest, 

 since the great part of the body, laden with eggs or sperms, is set 

 adrift and liberates these by breaking up in the waves; while the 

 head-end, remaining in the crevice of the coral-reef, regrows its 

 body for the next year's sacrifice. In this case death is evaded. 

 While it is one of the trends of evolution to lessen the physiological 

 strain of reproduction, some insects, such as Mayflies and many 

 butterflies, die a few hours after reproduction ; and the same is even 

 true of some comparatively large and strong animals, as lampreys 

 and eels. The exhaustion is fatal and the males are often victims as 

 well as their mates. But among higher animals there is a strong 

 tendency to reduce the sacrifice, not to speak of the fatality, of 

 reproduction. The familiar tragedy of the human mother's death 

 in child-birth must be regarded as altogether abnormal and 

 unnatural. 



THE RATE OF REPRODUCTION AND OF INCREASE.— The 



rate of reproduction depends upon the constitution of the individual 

 organism and on its immediate environment and nutrition. The rate 

 of reproduction in greenflies and rabbits is high; in elephants and 

 golden eagles it is very low. The rate of increase, which is much more 

 difficult to estimate, when a periodic census is not readily practicable, 

 depends upon the wide and complex conditions of life which are 

 often included in the phrase "the struggle for existence". Organisms 

 sometimes exhibit an extraordinary increase in numbers in favour- 

 able areas and seasons, witness plagues of voles or locusts; but man's 

 usual experience is that these sudden floods of life are soon arrested. 

 The increase meets checks of famine and weather, and a balance is 

 automatically restored. Even where species are becoming rare and 

 seem dwindling away, the reduction in numbers is usually very 

 gradual and slow, except when man ruthlessly interferes, as in the 

 case of the Great Auk and the Passenger Pigeon, the Quagga and 

 the American Bison. In natural conditions the decrease of the 

 population is occasionally sudden, as in the disappearance of the 



