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1859
1860
1861
1866
1869
1872

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1860
1861
1866
1869
1872

2 blocks not present in 1859 1860 1861; present in 1866 1869 1872
It is no valid objection to this conclusion or to the general belief that species in the course of time change, that certain Brachiopods have been but slightly modified from an extremely remote geological period, although no explanation can be given of this fact. It is not an insuperable difficulty that Foraminifera have not progressed in organisation, as insisted on by Dr. Carpenter, since that most ancient of all epochs the Laurentian formation of Canada; for some organisms would have to remain fitted for simple conditions of life, and what better for this end than these lowly organised Protozoa?

1 blocks not present in 1859 1860 1861 1872; present in 1866 1869
It is no great difficulty that fresh-water shells, as Professor Phillips has remarked, have remained almost unaltered from the time when they first appeared to the present day; but in this case we can see that these shells will have been subjected to less severe competition than the molluses which inhabit the far more extensive area of the sea with its innumerable inhabitants.

insists 1859 1860 1861 1866
and several other highly competent judges insist 1869 1872

in some degree parallel to 1859 1860 1861
in some degree parallel with 1866
nearly parallel with 1869 1872

proof. Seeing, for instance, that the oldest known mammals, reptiles, and fish strictly belong to their own proper classes, though some of these old forms are in a slight degree less distinct from each other than are the typical members of the same groups at the present day, it would be vain to look for animals having the common embryological character of the Vertebrata, until beds far beneath the lowest Silurian strata are discovered— a discovery of which the chance is very small. 1859
proof. 1860 1861 1866 1869 1872

areas , 1859 1861
areas . 1860
Areas, 1866 1869
Areas , 1872

species of the two countries could not have foreseen this result.
Agassiz insists that ancient animals resemble to a certain extent the embryos of recent animals
belonging to
of
the same classes;
and
or
that the geological succession of extinct forms is in some degree parallel to the embryological development of
existing
recent
forms. I must follow Pictet and Huxley in thinking that the truth of this doctrine is
very
very
far from proved. Yet I fully expect to see it hereafter confirmed, at least in regard to subordinate
groups
groups,
which have branched off from each other within comparatively recent times. For this doctrine of Agassiz accords
admirably well
well
with the theory of natural selection. In a future chapter I shall attempt to show that the adult differs from its embryo, owing to variations
having supervened
supervening
at a not early age, and
having been
being
inherited at a corresponding age. This process, whilst it leaves the embryo almost unaltered, continually adds, in the course of successive generations, more and more difference to the adult.
Thus the embryo comes to be left as a sort of picture, preserved by nature, of the
former
ancient
and less modified condition of
the animal.
the species.
each animal.
This view may be true, and yet
it
it
may never be capable of
full
full
proof. Seeing, for instance, that the oldest known mammals, reptiles, and fish strictly belong to their own proper classes, though some of these old forms are in a slight degree less distinct from each other than are the typical members of the same groups at the present day, it would be vain to look for animals having the common embryological character of the Vertebrata, until beds far beneath the lowest Silurian strata are discovered— a discovery of which the chance is very small.
On
On
the
the
Succession
Succession
of
of
the
the
same
same
Types
Types
within
within
the
the
same
same
areas ,