Origin of Species Variorum

→ real. 1859 1860 1861 1866 1869

as subversive of the theory. 1872

→ 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

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 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

→ OMIT 1869 1872

in each case 1859 1860 1861 1866

→ other species and genera 1866 1869 1872

species 1859 1860 1861

→ OMIT 1869 1872

from the earlier stages of descent, 1859 1860 1861 1866

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

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.

→ but without any nerve, and resting 1869

but which rest 1866

without any nerves, and resting 1872

conditions of life, then the difficulty of believing that a perfect and complex eye could

have been

formed by natural selection, though insuperable by our imagination,

can hardly

should not

cannot

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,

→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.

looking

searching

for the gradations

through

which

any

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

ancestors;

progenitors;

but this is scarcely ever possible, and we are forced →OMIT to look to →other species and genera of the same group, that is to the collateral descendants from the same

original

....

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

condi- tion.

condition.

But the state of the

same organ

organ even

in distinct classes may incidentally throw light on the steps by which it has been

perfected.

~~any~~

~~one~~

~~species.~~

↑

The simplest organ which can be called an eye consists of an optic nerve, surrounded by

pigment-cells,

pigment-cells

and covered

covered

by translucent skin, but without any lens or other refractive body. We may, however, according to M. Jourdain, descend even a step lower and find aggregates of pigment-cells, apparently serving as