360 Death and Dissolution of the Organism 



heart-beat must also cease, and gradually the different 

 tissues must undergo the dissolution characteristic 

 of death. While all the cells may be immortal they 

 are only so in the presence of oxygen and the nutritive 

 solution which the circulating blood furnishes. WitTi 

 the proper supply of oxygen cut off they can no longer 

 live. 



4. It is an unquestionable fact that each form has 

 a quite definite duration of life. Unicellular organisms 

 are immortal ; but for the higher organisms with sexual 

 reproduction the duration of life is almost as character- 

 istic as any morphological peculiarity of a species. 

 No species can exist unless the natural life of its in- 

 dividuals outlasts the period of sexual maturity; and 

 unless the average duration of life is long enough to 

 allow as many offspring to be brought into the world 

 as will compensate for loss by death. The male bee 

 dies before it is a year old, while the queen may live 

 several years. In a certain species of butterflies, the 

 Psychidas, the parthenogenetic female lays its eggs 

 while still in the cocoon and then dies without ever 

 leaving the cocoon. The imago of the ephemera 

 leaves the water in the evening, copulates, lets its eggs 

 fall into the water, and is dead the next morning. The 

 imperfect condition of their mandibles and alimentary 

 canal makes them unfit for a long duration of life. The 

 males of the rotifers which are devoid of organs of 

 digestion live but a few days. 



