| ↑ 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
the same classes;
that the geological succession of extinct forms is
→in some degree parallel to
the embryological development of
forms.
I must follow Pictet and Huxley in thinking that the truth of this doctrine is
far from proved. Yet I fully expect to see it hereafter confirmed, at least in regard to subordinate
which have branched off from each other within comparatively recent times. For this doctrine of Agassiz accords
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
at a not early age, and
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
and less modified condition of
This view may be true, and yet
may never be capable of
→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. |
|
→
areas
,
|
