Origin of Species Variorum

→ fishes. 1872

fish, or, for I do not know which view is now generally held, a part of the auditory apparatus has been worked in as a complement to the swimbladder. 1859 1860 1861 1866

fish. 1869

→ is no reason to doubt that the swimbladder 1869 1872

seems to me to be no great difficulty in believing that natural selection 1859 1860

seems to me to be no extreme difficulty in believing that natural selection 1861 1866

→ been converted into 1869 1872

converted a swimbladder into a 1859 1860 1861 1866

→ According to this view it may be inferred 1869 1872

I can, indeed, hardly doubt 1859 1860

On this view it may be inferred 1861 1866

→ and unknown prototype, which was 1869 1872

prototype, of which we know nothing, 1859 1860 1861 1866

→ but in the embryo the 1872

the 1859 1860 1861 1866

in the embryo the 1869

→ slits 1859 1860 1861 1869 1872

embryo the slits 1866

→ mark 1869 1872

marking in the embryo 1859 1860 1861

marking 1866

→ for instance, Landois has shown that 1872

in the same manner as, on the view entertained by some naturalists that 1859 1860 1861 1866

for instance, 1869

→ wings 1872

branchiæ and dorsal scales of Annelids are homologous with the wings and wing-covers 1859 1860 1861 1866

branchiæ and dorsal scales of Annelids are believed to be homologous with the wings and wing-covers 1869

→ are developed from the tracheæ; it is therefore highly 1872

it is 1859 1860 1861 1866

and it is not 1869

→ in this great class organs which once 1872

organs which at a very ancient period 1859 1860 1861 1866

with our existing insects, organs, which at an ancient period 1869

→ of the sack, together with 1869 1872

sack, including 1859 1860 1861

of the sack, including 1866

large folded branchiæ. 1859 1860

in the same relative position, large, much folded membranes, which freely communicate with the circulatory lacunæ of the sack and body, and which have been considered to be branchiæ by Prof. Owen and all other naturalists who have treated on the subject. 1861

in the same relative position with the frena, large, much-folded membranes, which freely communicate with the circulatory lacunæ of the sack and body, and which have been considered to be branchiæ by Prof. Owen and all other naturalists who have treated on the subject. 1866

in the same relative position with the frena, large, much-folded membranes, which freely communicate with the circulatory lacunæ of the sack and body, and which have been considered to be branchiæ by Prof. Owen and by all other naturalists who have treated on the subject. 1869

because it shows us clearly the highly important fact that an organ originally constructed for one

pur- pose,

purpose,

namely

namely,

flotation, may be converted into one for a

wholly

widely

different purpose,

namely

namely,

respiration. The

swim-bladder

swimbladder

has, also, been worked in as an accessory to the auditory organs of certain →fishes. All physiologists admit that the

swim-bladder

swimbladder

is homologous, or "ideally

similar,"

similar"

in position and structure with the lungs of the higher vertebrate animals: hence there →is no reason to doubt that the swimbladder has actually →been converted into

lung,

lungs,

organ

an organ

used exclusively for respiration.

→According to this view it may be inferred that all vertebrate animals

having

with

true lungs

have

are

descended by ordinary generation from an ancient →and unknown prototype, which was furnished with a floating apparatus or

swim-bladder.

swimbladder.

We can thus, as I infer from

Professor

....

Owens

Owen's

interesting description of these parts, understand the strange fact that every particle of food and drink which we swallow has to pass over the orifice of the trachea, with some risk of falling into the lungs, notwithstanding the beautiful contrivance by which the glottis is closed. In the higher

Vertebrata

Vertebrate

the branchiæ have wholly

disappeared—in

disappeared—but

disappeared—

→but in the embryo the →slits on the sides of the neck and the loop-like course of the arteries still →mark their former position. But it is conceivable that the now utterly lost branchiæ might have been gradually worked in by natural selection for some

quite

....

distinct purpose: →for instance, Landois has shown that the →wings of

insects,

insects

→are developed from the tracheæ; it is therefore highly

improbable

probable

that →in this great class organs which once served for

respiration,

respiration

have

actually been

been actually

converted into organs

for

flight.

In considering transitions of organs, it is so important to bear in mind the probability of conversion from one function to another, that I will give

one more

another

instance. Pedunculated cirripedes have two minute folds of skin, called by me the ovigerous frena, which serve, through the means of a sticky secretion, to retain the eggs until they are hatched within the sack. These cirripedes have no branchiæ, the whole surface of the body and →of the sack, together with the small frena, serving for respiration. The Balanidæ or sessile cirripedes, on the other hand, have no ovigerous frena, the eggs lying loose at the bottom of the sack,

within

the well-enclosed shell; but they

have

have,

→in the same relative position with the frena, large, much-folded membranes, which freely communicate with the circulatory lacunæ of the sack and body, and which have been considered by all naturalists to act as branchiæ. Now I think no one will dispute that the ovigerous frena in the one family are strictly homologous with the branchiæ of the other family; indeed,