CELL THEORIES. 135 



origin to a definite goal, may be observed in the 

 evolution of all animal forms in the history of the 

 globe. Such a doctrine alone is capable of explain- 

 ing all the facts of morphology, and giving to the 

 speculations of Darwin the backbone which they 

 require. [The reasons for it are stated in the fore- 

 going essay on the Evolutions of Organization. 

 It may be added here that such a doctrine is fav- 

 ourable rather than adverse to the supposition of a 

 genetic relationship of widely separate species. For 

 if not a textural unit has arisen save by genesis 

 from pre-existing units, and not an organism save 

 from pre-existing organisms, analogy, which is 

 however an uncertain guide, suggests that not a 

 species has arisen save from pre-existing species. 

 If the pedigree of man from inorganic matter has 

 during long ages passed through an ascending 

 series of forms, so also has individual manhood 

 passed through stages of development equally in- 

 ferior to the adult condition. But we enter on 

 another inquiry when we ask by what means the 

 highest development of organization has been 

 evolved both in the individual and in the world- 

 history of life, even supposing that genetic relation- 

 ship of all the parts be admitted as probable.] 



