Origin of Species Variorum

→ 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

is no reason to doubt that the swimbladder 1869 1872

→ converted a swimbladder into a 1859 1860 1861 1866

been converted into 1869 1872

→ I can, indeed, hardly doubt 1859 1860

On this view it may be inferred 1861 1866

According to this view it may be inferred 1869 1872

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

and unknown prototype, which was 1869 1872

→ the 1859 1860 1861 1866

in the embryo the 1869

but in the embryo the 1872

→ slits 1859 1860 1861 1869 1872

embryo the slits 1866

→ marking in the embryo 1859 1860 1861

marking 1866

mark 1869 1872

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

for instance, 1869

for instance, Landois has shown that 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

wings 1872

→ it is 1859 1860 1861 1866

and it is not 1869

are developed from the tracheæ; it is therefore highly 1872

→ organs which at a very ancient period 1859 1860 1861 1866

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

in this great class organs which once 1872

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 →seems to me to be no great difficulty in believing that natural selection has actually →converted a swimbladder into a

lungs,

lung,

an organ

organ

used exclusively for respiration.

→I can, indeed, hardly doubt that all vertebrate animals

with

having

true lungs

are

have

descended by ordinary generation from an ancient →prototype, of which we know nothing, furnished with a floating apparatus or

swim-bladder.

swimbladder.

We can thus, as I infer from

~~Professor~~

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

Vertebrate

Vertebrata

the branchiæ have wholly

disappeared—in

disappeared—but

disappeared—

→the →slits on the sides of the neck and the loop-like course of the arteries still →marking in the embryo 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~~

quite

distinct purpose: →in the same manner as, on the view entertained by some naturalists that the →branchiæ and dorsal scales of Annelids are homologous with the wings and wing-covers of

insects

insects,

→it is

improbable

probable

that →organs which at a very ancient period 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

another

one more

instance. Pedunculated cirripedes have two minute folds of skin,