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1859
1860
1861
1866
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1872

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1859
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1872

→ have left behind them 1859 1860 1861 1866
which formerly lived 1869 1872
→ the 1859 1860 1861 1866
have left behind them the 1869 1872
→ have descended from 1859 1860 1861
are the descendants of 1866 1869 1872
→ constituting the six 1859 1860 1861
which constitute the several species of the 1866 1869
which constitute the 1872
→ genera. 1859 1860 1861
genera; 1866 1869
genera containing the several species; 1872
→ the 1859 1860 1861
each of the 1866
each 1869 1872
→ genera have all 1859 1860 1861
genera having 1866
genus having 1869 1872
→ which would probably 1859 1860 1861
and this probably would 1866
and this probably will 1869
and this will 1872
It may be asked in ridicule, whether I suppose that the megatherium and other allied huge
monsters,
monsters
→have left behind them in South
America
America,
→the sloth, armadillo, and anteater, as their degenerate descendants. This cannot for an instant be admitted. These huge animals have become wholly extinct, and have left no progeny. But in the caves of Brazil, there are many extinct species which are closely allied in size and in
all other
other
characters to the species still living in South America; and some of these fossils may
have been
be
the actual progenitors of
the living
living
species. It must not be forgotten that, on
our
my
theory, all the species of the same genus →have descended from some one species; so
that,
that
if six genera, each having eight species, be found in one geological formation, and in
a
the next
succeeding formation there be six other allied or representative genera
each with
with
the same number of species, then we may conclude that
generally only
only
one species of each of the
six
six
older genera has left modified descendants, →constituting the six new →genera.
the
The
other seven species of →the old →genera have all died out and
have
have
left no progeny. Or, →which would probably be a far commoner case, two or three species
in
of
only two
two
or three
alone
alone
of the six older genera will
be
have been
the parents of the
six
six
new
genera:
genera;
the other
old
old
species and the other
old whole
whole
genera
old genera
having become utterly extinct. In failing orders, with the genera and species decreasing in
numbers
numbers,
as
apparently
apparently
is the case
with
of
the Edentata of South America, still fewer genera and species will
leave
have left
modified blood-descendants.
Summary
Summary
of
of
the
the
preceding
preceding
and
and
present
present
Chapters .—
Chapter. —
Chapter .
Chapter .
Chapters .
Chapters. —
I have attempted to show that the geological record is extremely imperfect; that only a small portion of the globe has been geologically explored with care; that