284 THE LESSON OF EVOLUTION 



.sunlight, and building up organic compounds. The 

 other half is employed in changing the chemical 

 energy thus accumulated into mechanical move- 

 ments, to which, for the sake of brevity, the com- 

 prehensive name of ' ' locomotion ' ' may be given ; 

 for under this- name I wish to include the internal 

 movements of the cell-contents, as well, as the exter- 

 nal movements of the cells themselves. 



The nutrition of animals is due to the absorption 

 of the products of assimilation, and is therefore here 

 included under locomotion. Eeproduction is due 

 to the movements of the contents of certain cells, 

 and it also comes under the heading of locomotion. 

 Sometimes the movements are sufficiently rapid for 

 instant recognition ; at other times they are very 

 slow, as in the germination of seeds, and we have 

 to wait for days or weeks before we know whether 

 they are alive or dead. These two functions of assi- 

 milation and locomotion are performed by chloro- 

 phyll and protoplasm respectively ; and one of these 

 substances cannot perform the functions of the other. 

 Assimilation is a chemical action, and is easily 

 recognised by chemical tests. We cannot follow the 

 reactions, neither do we know how the organic com- 

 pounds of carbon, hydrogen, and oxygen are formed, 

 but these processes may be explained any day by the 

 chemist. However, chlorophyll is not universal in 

 living matter. It is found chiefly in plants, but also 

 in some groups of animals ; while protoplasm never 

 fails to be present wherever life is recognised. 

 Trom this we must suppose that protoplasm is the 

 fundamental living substance, and that chlorophyll 



