Origin of Species Variorum

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

For the embryo is the animal in its less modified state; and in so far it reveals the structure of its progenitor.

→ or more groups 1866 1869 1872

groups 1859 1860 1861

→ in their adult condition, if 1872

if 1859 1860 1861 1866 1869

→ closely 1866 1869 1872

the same or 1859 1860 1861

→ one parent-form, 1869 1872

the same or nearly similar parents, 1859 1860 1861

the same parent-form, 1866

→ OMIT 1866 1869 1872

in that degree 1859 1860 1861

→ descent; but dissimilarity in embryonic development does not prove discommunity of descent, for in one of two groups the developmental stages may have been suppressed, or may have been so greatly modified through adaptation to new habits of life, as to be no longer recognisable. 1869 1872

descent. 1859 1860 1861

descent; but dissimilarity in embryonic development does not prove discommunity of descent, for in one of two groups all the developmental stages may have been suppressed, or may have been so greatly modified as no longer to be recognised, through adaptations, during the earlier periods of growth, to new habits of life. 1866

→ embryo often 1872

embryonic state of each species and group of species partially 1859 1860 1861

embryonic state of each species and group of species 1866

structure of the embryo generally 1869

→ more or less plainly the 1869 1872

the 1859 1860 1861

more or less completely the 1866

→ and ancient progenitor of the group, 1872

ancient progenitors, 1859 1860 1861 1866

and ancient progenitor, 1869

→ so often resemble in their adult state 1872

of life should resemble 1859 1860 1861 1866

so often resemble 1869

→ OMIT 1869 1872

their descendants,— our 1859 1860 1861

our 1866

→ species of the same class. 1872

species. 1859 1860 1861

species, their descendants. 1866

species in the same class. 1869

→ and we may hope hereafter 1872

but I am bound to confess that I only hope 1859 1860 1861 1866

and I hope 1869

→ the law proved 1872

the law hereafter proved 1859 1860 1861 1866

it hereafter shown in most cases 1869

→ of the progenitor of the group 1872

now supposed to be represented in many embryos, 1859

now supposed to be represented in existing embryos, 1860 1861 1866

OMIT 1869

→ OMIT 1866 1869 1872

in a long course of modification 1859 1860 1861

→ period of growth, or 1861 1869 1872

age, or 1859 1860

period of growth, nor 1866

→ may be true, but yet, owing 1869 1872

of resemblance of ancient forms of life 1859 1860 1861 1866

→ OMIT 1869 1872

embryonic stages of recent forms, may be true, but yet, owing to the 1859 1860 1861 1866

→ such larvæ 1872

these in their larval condition 1869

→ still more ancient 1872

ancient 1869

→ variations 1872

slight modifications not appearing, 1859 1861

slight modifi- cations not appearing, 1860

slight modifications not having appeared, 1866

modifications 1869

→ having appeared at a not very 1872

at a very 1859 1860 1861 1866

not having appeared at an 1869

→ of life, and having been 1869 1872

in the life of each, though perhaps caused at the earliest, and being 1859 1860 1861

in the life of each, though perhaps caused at the earliest, and having been 1866

→ as 1859 1860 1861 1869 1872

of an animal as 1866

→ progenitor, either in its adult or larval state, of all the members of the same 1866 1869 1872

common parent-form of each 1859 1860 1861

than that of the adult. ↑ In two →or more groups of

animal,

animals,

however much they may

at present

....

differ from each other in structure and

habits,

habits

→in their adult condition, if they pass through →closely similar embryonic stages, we may feel

almost assured

assured

that they

have both

have

all are

descended from →one parent-form, and are therefore →OMIT closely related. Thus, community in embryonic structure reveals community of →descent; but dissimilarity in embryonic development does not prove discommunity of descent, for in one of two groups the developmental stages may have been suppressed, or may have been so greatly modified through adaptation to new habits of life, as to be no longer recognisable. Even in groups, in which the adults have been modified to an extreme degree, community of origin is often revealed by the structure of the larvæ; we have seen, for instance, that cirripedes, though externally so like shell-fish, are at once known by their larvæ to belong to the great class of crustaceans. As the →embryo often shows us →more or less plainly the structure of

their

its

the

less modified →and ancient progenitor of the group, we can

clearly

....

see why ancient and extinct forms →so often resemble in their adult state the embryos of →OMIT existing →species of the same class. Agassiz believes this to be a

law

universal law

of nature; →and we may hope hereafter to see →the law proved true. It

can

can,

however, be

proved true

only in

those cases

alone

....

in which the ancient

state,

state

→of the progenitor of the group has

~~not~~

not

been

obliterated,

obliterated

wholly obliterated

wholly obliterated,

neither

either

the

....

successive variations →OMIT having

super- vened

supervened

at a very early →period of growth, or by

the

such

variations having been inherited at an earlier

period

age

than that at which they first appeared. It should also be borne in mind, that the

supposed

....

law →may be true, but yet, owing to the →OMIT geological record not extending far enough back in time, may remain for a long period, or for ever,

in- capable

incapable

of demonstration. The law will not

hold

strictly hold

good in those cases in which an ancient form became adapted in its larval state to some special line of life, and transmitted the same larval state to a whole group of descendants; for →such larvæ will not resemble any →still more ancient form in its adult state.

Thus, as it seems to me, the leading facts in embryology, which are second

in importance

....

to none in

natural history,

importance,

are explained on the principle of →variations in the many descendants from some one ancient progenitor, →having appeared at a not very early period →of life, and having been inherited at a corresponding

not early

....

period. Embryology rises greatly in interest, when we

thus

....

look at the embryo →as a picture, more or less obscured, of the →progenitor, either in its adult or larval state, of all the members of the same great

class

class.

....

animals.

....