| All the many forms, extinct and recent, descended from
make, as before remarked, one order; and this order, from the continued effects of extinction and divergence of character, has become divided into several sub-families and families, some of which are supposed to have perished at different periods, and some to have endured to the present day. |
| By looking at the diagram we can see that if many of the extinct
supposed to be
in the successive formations, were discovered at several points low down in the series, the three existing families on the uppermost line would be rendered less distinct from each other. If, for instance, the genera
a
1
,
a
5
, →
a
10
,
f
8
,
m
3
, →
m
6
,
m
9
,
were
these three families would be so closely linked together that they probably would have to be united into one great family, in nearly the same manner as has occurred with ruminants and
Yet he who objected to
→call
the extinct
which thus
the living genera of three
→together, intermediate in character,
would be
→justified, as
they are intermediate, not directly, but only by a long and circuitous course through many widely different forms. If many extinct forms were to be discovered above one of the middle horizontal lines or geological formations— for instance, above No. VI.— but none from beneath
line, then only
two
→families
on the left
→
a
14
,
&c., and
→
b
14
,
&c.) would have to be united into
and
→
the two other families (namely,
a
14
to
f
14
now including five genera, and
o
14
to
m
14
) would yet remain distinct.
These two families, however, would be less distinct from each other than they were before the
|
