III.] LIFE AND DEATH. l6l 



IV. The fundamental biogenetic law applies only to multi- 

 cellular beings ; it does not apply to unicellular forms of life. 

 This depends on the one hand upon the mode of reproduction 

 by fission which obtains among the Monoplastides (unicellular 

 organisms), 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 or- 

 ganisms). 



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 

 reproduction 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 fine 

 from the first and lowest forms. 



M 



