LIFE AND DEATH. 159 



ganisms), and on the other upon the necessity, induced by sexual 

 reproduction, for the maintenance of a unicellular stage in the 

 development of the Polyplastides (multicellular organisms). 



V. Death itself, and the longer or shorter duration of life, 

 both depend entirely on adaptation. Death is not an essential 

 attribute of living- matter ; it is neither necessarily associated with 

 reproduction, nor a necessary consequence of it. 



In conclusion, I should wish to call attention to an idea which is 

 rather implied than expressed in this essay : it is, that reproduc- 

 tion did not first make its appearance coincidently with death. 

 Reproduction is in truth an essential attribute of living- matter, just 

 as is the growth which gives rise to it. It is as impossible to 

 imagine life enduring without reproduction as it would be to 

 conceive life lasting* without the capacity for absorption of food 

 and without the power of metabolism. Life is continuous and 

 not periodically interrupted : ever since its first appearance upon 

 the earth, in the lowest organisms, it has continued without break ; 

 the forms in which it is manifested have alone undergone change. 

 Every individual alive to day even the very highest is to be 

 derived in an unbroken line from the first and lowest forms. 



