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1859
1860
1861
1866
1869
1872

Compare with:
1860
1861
1866
1869
1872

but 1859 1860 1861
and only partially 1866 1869 1872

from other groups, as all would blend together by steps as fine as those between the finest existing varieties, nevertheless 1859 1860
from other groups, as all would blend together by steps as fine as those between existing varieties, nevertheless 1861
from other groups, as all would be blended together by steps as fine as those between existing varieties, nevertheless 1866
still 1869 1872

Every intermediate link between these eleven genera and their primordial parent, and every intermediate 1859 1860 1861 1866
with every 1869 1872

of their descendants, may be supposed to be 1859 1860 1861 1866
OMIT 1869 1872

to be as fine as 1859 1860 1861 1866
not greater than 1869 1872

or these parents from their ancient and unknown progenitor. 1859 1860 1861 1866
and descendants. 1869 1872

on 1859 1860 1861 1866
would be natural; for, on 1869 1872

from A, or from I, 1859 1860 1861 1866
for instance, from A, 1869 1872

We shall certainly 1859 1860
We shall assuredly 1861 1866
Assuredly we shall 1869 1872

together by
a
a
long
long,
but
broken
broken,
chains
chain
of affinities. Extinction has only
defined the
separated
the groups:
groups:
it has by no means made them; for if every form which has ever lived on this earth were suddenly to reappear, though it would be quite impossible to give definitions by which each group could be
distinguished,
distinguished
from other groups, as all would blend together by steps as fine as those between the finest existing varieties, nevertheless a natural classification, or at least a natural arrangement, would be possible. We shall see this by turning to the
diagram;
diagram:
the letters, A to L, may represent eleven Silurian genera, some of which have produced large groups of modified
descendants,
descendants.
Every intermediate link between these eleven genera and their primordial parent, and every intermediate link in each branch and sub-branch of their descendants, may be supposed to be still alive; and the links to be as fine as those between
existing
the finest
varieties. In this case it would be quite impossible to give
any
any
definitions
definition
by which the several members of the several groups could be distinguished from their more immediate
parents
parents;
or these parents from their ancient and unknown progenitor. Yet the
natural
natural
arrangement in the diagram would still hold
good
good;
and
and,
on the principle of inheritance, all the forms
descended,
descended
from A, or from I, would have something in common. In a tree we can
distinguish
specify
this or that branch, though at the actual fork the two unite and blend together. We could not, as I have said, define the several groups; but we could pick out types, or forms, representing most of the characters of each group, whether large or small, and thus give a general idea of the value of the differences between them. This is what we should be driven to, if we were ever to succeed in collecting all the forms in any
one class
class
which have lived throughout all time and space. We shall certainly never succeed in making