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See page in:
1859
1860
1861
1866
1869
1872

Compare with:
1860
1861
1866
1869
1872

→ and similar considerations, but chiefly 1859 1860 1861 1866
considerations, 1869 1872
→ ideas on many points, which 1859 1860 1861 1866
knowledge effected by 1869 1872
→ numbers of species 1859 1860 1861 1866
many species in several 1869
species belonging to several 1872
→ same group, 1859 1860 1861
same group 1866
main divisions of the animal kingdom 1869 1872
→ Silurian trilobites have 1859 1860 1861 1866
Silurian trilobites are 1869
Cambrian and Silurian trilobites are 1872
→ of the orders to which they belong, 1859 1860 1861
belonging to the same group which have subsequently appeared, 1866
belonging to the same groups which have subsequently appeared, 1869 1872
here they would remain confined, until some of the species became adapted to a cooler climate, and were enabled to double the
Southern
southern
capes of Africa or Australia, and thus reach other and distant seas.
From these →and similar considerations, but chiefly from our ignorance of the geology of other countries beyond the confines of Europe and the United
States,
States;
and from the revolution in our palæontological →ideas on many points, which the discoveries of
even
even
the last dozen
years,
years
have effected,
have effected,
it seems to me to be about as rash
in us
in us
to dogmatize on the succession of organic
forms
beings
throughout the world, as it would be for a naturalist to land for five minutes on
a
some one
barren point in Australia, and then to discuss the number and range of its productions.
On
On
the
the
sudden
sudden
Appearance
appearance
of
of
Groups
groups
of
of
allied
allied
Allied
Species
Species
in
in
the
the
lowest
lowest
known
known
Fossiliferous
fossiliferous
Strata .
strata .—
There is another and allied difficulty, which is much
more serious.
graver.
I allude to the manner in which →numbers of species of the →same group, suddenly appear in the lowest known fossiliferous rocks. Most of the arguments which have convinced me that all the existing species of the same group
are
have
descended from
a single
one
progenitor, apply with
nearly
nearly
equal force to the earliest known species. For instance,
it
I
cannot
be doubted
doubt
that all the →Silurian trilobites have descended from some one crustacean, which must have lived long before the
Cambrian
Silurian
age, and which probably differed greatly from any known animal. Some of the most ancient
Silurian
Silurian
animals, as the Nautilus, Lingula,
&c,
&c.,
do not differ much from living species; and it cannot on
our
my
theory be supposed, that these old species were the progenitors of all the species →of the orders to which they belong, for they
are
do
not
present characters
present characters
in any degree intermediate
in character.
between them.