apital letters, converging in
sub-branches downwards towards a single point; this point represents
a species, the supposed progenitor of our several new sub-genera and
genera.

It is worth while to reflect for a moment on the character of the new
species F14, which is supposed not to have diverged much in character,
but to have retained the form of (F), either unaltered or altered only
in a slight degree. In this case its affinities to the other fourteen
new species will be of a curious and circuitous nature. Being descended
from a form that stood between the parent-species (A) and (I),
now supposed to be extinct and unknown, it will be in some degree
intermediate in character between the two groups descended from these
two species. But as these two groups have gone on diverging in character
from the type of their parents, the new species (F14) will not be
directly intermediate between them, but rather between types of the two
groups; and every naturalist will be able to call such cases before his
mind.

In the diagram each horizontal line has hitherto been supposed to
represent a thousand generations, but each may represent a million or
more generations; it may also represent a section of the successive
strata of the earth's crust including extinct remains. We shall, when we
come to our chapter on geology, have to refer again to this subject,
and I think we shall then see that the diagram throws light on the
affinities of extinct beings, which, though generally belonging to the
same orders, families, or genera, with those now living, yet are often,
in some degree, intermediate in character between existing groups; and
we can understand this fact, for the extinct species lived at various
remote epochs when the branching lines of descent had diverged less.

I see no reason to limit the process of modification, as now explained,
to the formation of genera alone. If, in the diagram, we suppose the
amount of change represented by each successive group of diverging
dotted lines to be great, the forms marked a14 to p14, those marked
b14 and f14, and those marked o14 to m14, will form three very distinct
genera. We shall also have two very distinct genera descended from (I),
differing widely from the descendants of (A). These two groups of genera
will thus form two distinct families, or orders, according to the amount
of divergent modification supposed to be represented in the diagram. And
the two new families, or orders, a