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.] 
