Origin of Species Variorum

→ real. 1859 1860 1861 1866 1869

as subversive of the theory. 1872

→ several facts make me suspect that any sensitive nerve may be rendered sensitive to light, and likewise to those coarser vibrations of the air which produce sound. 1859 1860

several facts make me suspect that nerves sensitive to touch may be rendered sensitive to light, and likewise to those coarser vibrations of the air which produce sound. 1861

as some of the lowest organisms, in which nerves cannot be detected, are known to be sensitive to light, it does not seem impossible that certain elements in their tissues or sarcode should have become aggregated and developed into nerves endowed with special sensibility to its action. 1866

as some of the lowest organisms, in which nerves cannot be detected, are known to be sensitive to light, it does not seem impossible that certain elements in the sarcode, of which they are mainly composed, should become aggregated and developed into nerves endowed with this special sensibility. 1869

as some of the lowest organisms, in which nerves cannot be detected, are capable of perceiving light, it does not seem impossible that certain sensitive elements in their sarcode should become aggregated and developed into nerves, endowed with this special sensibility. 1872

→ in each case 1859 1860 1861 1866

OMIT 1869 1872

→ species 1859 1860 1861

other species and genera 1866 1869 1872

→ from the earlier stages of descent, 1859 1860 1861 1866

OMIT 1869 1872

↑ 1 blocks not present in 1859 1860 1861 1866; present in 1869 1872

But the state of the organ even in distinct classes may incidentally throw light on the steps by which it has been perfected in any one species.

→ Amongst existing Vertebrata, we find but a small amount of gradation 1859 1860 1861

But the state of the same organ even 1866

→ structure 1859 1860 1861

other main divisions 1866

→ eye, and from fossil species we can learn nothing on this head. 1859 1860

eye (though in the fish Amphioxus, the eye is in an extremely simple condition without a lens), and from fossil species we can learn nothing on this head. 1861

organic world may incidentally throw light on the steps by which it has been perfected. 1866

selection, though insuperable by our imagination,

cannot

should not

can hardly

be considered →real. How a nerve comes to be sensitive to light, hardly concerns us more than how life itself

~~first~~

first

originated; but I may remark

that,

that

→several facts make me suspect that any sensitive nerve may be rendered sensitive to light, and likewise to those coarser vibrations of the air which produce sound.

searching

looking

for the gradations

through

which

any

organ in any species has been perfected, we ought to look exclusively to its lineal

progenitors;

ancestors;

but this is scarcely ever possible, and we are forced →in each case to look to →species of the same group, that is to the collateral descendants from the same

~~original~~

original

parent-form, in order to see what gradations are possible, and for the chance of some gradations having been transmitted →from the earlier stages of descent, in an unaltered or little altered

condi- tion.

condition.

↑ →Amongst existing Vertebrata, we find but a small amount of gradation in the →structure of the →eye, and from fossil species we can learn nothing on this head. In this great class we should probably have to descend far beneath the lowest known fossiliferous stratum to discover the earlier stages, by which the eye has been perfected.

In the Articulata we can commence a series with an optic nerve merely coated with pigment, and without any other mechanism; and from this low stage, numerous gradations of structure, branching off in two fundamentally different lines, can be shown to exist, until we reach a moderately high stage of perfection. In certain crustaceans, for instance, there is a double cornea, the inner one divided into facets, within each of which there is a lens-shaped swelling. In other crustaceans the transparent cones which are coated by pigment, and which properly act only by excluding lateral pencils of light, are convex at their upper ends