Origin of Species Variorum

→ 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

→ in the embryo the 1869

the 1859 1860 1861 1866

but in the embryo the 1872

→ slits 1859 1860 1861 1869 1872

embryo the slits 1866

→ mark 1869 1872

marking in the embryo 1859 1860 1861

marking 1866

→ for instance, 1869

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

for instance, Landois has shown that 1872

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

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

wings 1872

→ and it is not 1869

it is 1859 1860 1861 1866

are developed from the tracheæ; it is therefore highly 1872

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

organs which at a very ancient period 1859 1860 1861 1866

in this great class organs which once 1872

→ of the sack, together with 1869 1872

sack, including 1859 1860 1861

of the sack, including 1866

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

are

have

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

Vertebrate

Vertebrata

the branchiæ have wholly

disappeared—

disappeared—in

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

insects

insects,

→and it is not

probable

improbable

that →with our existing insects, organs, which at an ancient period served for

respiration

respiration,

have

been actually

actually been

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