Origin of Species Variorum

→ dimorphic forms, and 1869 1872

and 1859 1860 1861

dimorphic states, and 1866

→ differ from each other 1872

be 1859 1860 1861 1866 1869

→ different species 1869 1872

homologous organs, to whatever purpose applied, 1859 1860 1861 1866

→ same class in their homologous organs, to whatever purpose applied; 1869 1872

different species of a class; 1859 1860 1861

different species in the same class; 1866

→ serial and lateral homologies 1872

homologous parts constructed on the same pattern 1859 1860 1861 1866

homologous parts 1869

→ close resemblance in the 1869 1872

resemblance in an 1859 1860 1861 1866

→ parts which are homologous, and which 1869 1872

homologous parts, which 1859 1860 1861 1866

→ OMIT 1869 1872

from each other 1859 1860 1861 1866

→ of the 1872

in different species of a class of the 1859 1860 1861

in different species of the same class of the 1866

in allied though very distinct species of their 1869

→ in allied though distinct species, though 1872

though 1859 1860 1861 1866 1869

→ a greater or less degree in relation 1869 1872

relation 1859 1860 1861 1866

→ with their modifications 1869 1872

through the principle of modifications being 1859 1860 1861 1866

→ a corresponding early 1872

corresponding 1859 1860 1861 1866

a corresponding 1869

→ through natural selection, 1869 1872

selection, 1859 1860 1861 1866

→ might even 1869 1872

and their final abortion, present to us no inexplicable difficulties; on the contrary, their presence might 1859 1860 1861

and their final abortion, present to us no inexplicable difficulties; on the contrary, their pre- sence might 1866

→ have been 1869 1872

have been even 1859 1860 1861

even have been 1866

→ a natural arrangement must be 1869 1872

an arrangement is only so far natural as it is 1859 1860 1861 1866

→ OMIT 1869 1872

of organic beings, 1859 1860 1861 1866

selection, with

its

the

contingencies of extinction and divergence of character. In considering this view of classification, it should be borne in mind that the element of descent has been universally used in ranking together the sexes, ages, →dimorphic forms, and acknowledged varieties of the same species, however

different

much

they may →differ from each other in structure. If we extend the use of this element of descent,— the

only

one

certainly known cause of similarity in organic beings,— we shall understand what is meant by the

natural

Natural

system:

System:

it is genealogical in its attempted arrangement,

and

with

the grades of acquired difference

are marked

marked

by the

terms

terms,

varieties, species, genera, families, orders, and classes.

On this same view of descent with modification,

all

most of

the great facts in Morphology become intelligible,— whether we look to the same pattern displayed

the →different species of the →same class in their homologous organs, to whatever purpose applied; or to the →serial and lateral homologies in each individual animal and plant.

On the principle of successive slight variations, not necessarily or generally supervening at a very early period of life, and being inherited at a corresponding period, we can understand the

great

....

leading facts in Embryology; namely, the →close resemblance in the individual embryo of the →parts which are homologous, and which when matured

will

....

become widely different →OMIT in structure and function; and the resemblance →of the homologous parts or

organs,

organs

→in allied though distinct species, though fitted in the adult

members

state

for

purposes

habits

as different as

possible.

is possible.

Larvæ are active embryos, which have

become

been

specially modified in →a greater or less degree in relation to their habits of life, →with their modifications inherited at →a corresponding early

ages.

age.

this

these

same

principle—

principles,—

and bearing in mind, that when organs are reduced in size, either from disuse or →through natural selection, it will generally be at that period of life when the being has to provide for its own wants, and bearing in mind how strong is the

principle

force

of inheritance— the occurrence of rudimentary organs →might even →have been anticipated. The importance of embryological characters and of rudimentary organs in classification is intelligible, on the view that →a natural arrangement must be genealogical.

Finally, the several classes of facts which have been considered in this chapter, seem to me to proclaim so plainly, that the

inumerable

innumerable

species,

genera,

genera

and

families

families,

→OMIT with which this world is peopled,

have

are

all descended, each within its own class or group, from common parents, and have all been modified in the course of descent, that I should without hesitation adopt this view, even if it were unsupported by

any other

other