40 ESSAYS SCIENTIFIC AND PHILOSOPHICAL. 



less "conscious of their own existence" than the 

 protozoa? Have we any right to assert either 

 that the brute has an " ego!' or that the plant has 

 no sensation? The line which separates living 

 from not living is at present as clear as that which 

 separates man from brute ; but when Mr. Wallace 

 talks of "sensation" and the "ego" of conscious 

 and unconscious life, he passes into the region of 

 metaphysics, where he is as little competent to 

 lead as we are willing to follow. 



