Origin of Species Variorum

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

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.

→ look for gradations, we 1866

OMIT 1869 1872

→ which sometimes forms 1866

the latter sometimes forming 1869 1872

→ cones surrounded by pigment, which form the 1866

facets on the cornea of the 1869

facets on the cornea of their 1872

form true lenses, and that the cones include curiously modified nervous filaments. 1869 1872

→ Altogether so diversified is the structure of the eye 1866

But these organs 1869

→ that Müller makes 1866

are so much diversified that Müller formerly made 1869

→ with seven subdivisions, 1866

OMIT 1869

→ and he adds 1866

with seven subdivisions, besides 1869

→ When we reflect on 1866 1869 1872

With 1859 1860 1861

→ and imperfectly, with respect to the wide, diversified, and graduated range of structure 1866

and imperfectly given, which show that there is much graduated diversity 1859 1860

and imperfectly given, which show how much graduated diversity 1861

with respect to the wide, diversified, and graduated range of structure 1869 1872

→ in 1859 1860 1866 1869 1872

there is in 1861

→ the existing Articulata; and when we bear 1866

living crustaceans, and bearing 1859 1860

our existing crustaceans, and bearing 1861

the lower animals; and when we bear 1869 1872

→ all living forms must be in comparison with 1866 1872

living animals is in proportion to 1859 1860 1861

all the forms now living must be in comparison with 1869

gain the first and by far the most important step towards the formation of a

true,

true

picture-forming eye; for we have only to place the naked extremity of the optic nerve, which in some of the lower animals lies deeply buried in the

body,

body

and in some near the surface, at the right distance from the concentrating apparatus, and an image

will

must

be formed on it. ↑

In the great class of the Articulata,

we →look for gradations, we may start from an optic nerve simply coated with pigment, →which sometimes forms a sort of pupil, but

destitute of a lens or other optical contrivance. From this point we have to make a rather wider stride than in the case of the above-mentioned star-fish, and we come to certain Crustaceans in which the eyes are covered by a double cornea,—the external membrane smooth and the internal one divided into facets,—within the substance of which, as Milne Edwards states, " renflemens lenticulaires paraissent s'être développés; " and these lenses can sometimes be detached in a layer distinct from the cornea. With insects it is now known that the numerous →cones surrounded by pigment, which form the great compound

eyes

eyes,

→are filled with transparent refractive matter, and these cones produce images; but in addition, in certain beetles the facets of the cornea are slightly convex both externally and internally,—that is, are lens-shaped. →Altogether so diversified is the structure of the eye in the Articulata →that Müller makes three main

classes

classes,

→with seven subdivisions, of compound

eyes

eyes,

→and he adds a fourth main class of aggregated

simple eyes.

simple-eyes.

→When we reflect on these facts, here

far

given much

~~given~~

given

too

briefly,

briefly

→and imperfectly, with respect to the wide, diversified, and graduated range of structure →in the eyes of →the existing Articulata; and when we bear in mind how small the number of →all living forms must be in comparison with