328 Extracts from Mr. Bentham’s Address 
of the Horse, but we can understand more readily the aneonaie 
identity of certain species of plants inhabiting widely diss 
States and Japan respetvely —an argument which has 
appeared to me to have considerable weight—was this :—if dis- 
severance and subsequent isolation result necessarily in a grad- 
ual modification by natural “np how is it that when all 
are subjected to the same influences, the descendants of some 
races have become st generically distinct in the two regions, 
whilst others are univ sjeowdi acknowledged as congeners, but 
specifically distinct, he other : ae are only slight varieties 
ave remained a Sey epee To this we can now 
flora and fauna of a country to a distant region, or, what comes 
to the same thing, change the external conditions of that flora 
and fauna, as to climate, physical influences, natural enemies, 
or other causes. of destruction, means of protec ction, &e., W 
we sae several generations, but with decreasing vigor, 
n_ the course % years or ages, eretialy * die out, to be re re- 
generations and a an IS oe species may be 
formed. And some few races might find themselves quite as 
hap 0 vigorous under their new circumstances as — 
om upon these meen by the _— investigations and by 
the numerous observations called forth b a development of 
