Origin of Species Variorum

↑ 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. 1860 1861 1866 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

→ far 1860 1861

rich in fossils are discovered far 1866 1869 1872

→ Silurian strata are discovered— 1860 1861

Silurian stratum— 1866 1869

Cambrian strata— 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

the same classes;

and

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

may never be capable of

~~full~~

full

→proof. Seeing, for instance, that the oldest known mammals, reptiles, and

fishes

fish

strictly belong to their

~~own~~

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~~

very

small.

the

Succession

the

same

Types

within

the

same