Chap. XIII. 
CLASSIFICATION. 
421 
degree ; tliey may metapliorically be called cousins to 
the same millionth degree; yet they differ widely 
and in different degrees from each other. The forms 
descended from A, now broken up into two or three 
families, constitute a distinct order from those de¬ 
scended from I, also broken up into two families. Nor 
can the existing species, descended from A, be ranked 
in the same genus with the parent A; or those from 
I, with the parent I. But the existing genus f may 
be supposed to have been but slightly modified; and 
it will then rank with the parent-genus F; just as 
some few still living organic beings belong to Silurian 
genera. So that the amount or value of the differ¬ 
ences between organic beings all related to each other 
in the same degree in blood, has come to be widely 
different. Nevertheless their genealogical arrange¬ 
ment remains strictly true, not only at the present 
time, but at each successive period of descent. All 
the modified descendants from A will have inherited 
something in common from their common parent, as 
will all the descendants from I; so will it be with each 
subordinate branch of descendants, at each successive 
period. If, however, we choose to suppose that any of 
the descendants of A or of I have been so much modi¬ 
fied as to have more or less completely lost traces of 
their parentage, in this case, their places in a natural 
classification will have been more or less completely lost, 
—as sometimes seems to have occurred with existing 
organisms. All the descendants of the genus F, along 
its whole line of descent, are supposed to have been 
but little modified, and they yet form a single genus. 
But this genus, though much isolated, will still occupy 
its proper intermediate position; for F originally was 
intermediate in character between A and I, and the 
several genera descended from these two genera will 
