120 A PRIMER OF BIOLOGY 



tion of organic compounds. Both are sensitive to 

 stimuli, both multiply their kind. Both have the 

 power of movement, although not in equal degree, 

 and the skeletons of both are constructed in accord- 

 ance with the same laws. Finally, we have seen that 

 there is good evidence for believing that organisms 

 are related to each other in some cases, less, in 

 other cases, more distantly but that all of them may 

 be regarded as terminal twigs of the infinitely branched 

 trunks of the bifurcate tree of life. It must be left 

 to other volumes of this series to connect the organic 

 \vorld with the inorganic, from which in the long run 

 both obtain their nutriment, and by whose laws they 

 also are governed. 



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