Origin of Species Variorum

→ And as the whole amount of modification will have been effected by slight successive steps, we need not wonder at discovering in 1859 1860 1861

And as the whole amount of modification will have been effected by successive slight steps, we need not wonder at discovering in 1866

Consequently 1869 1872

→ or organs, a certain degree of fundamental resemblance, retained by the strong principle 1859 1860

or organs a certain degree of fundamental resemblance, retained by the strong principle 1861 1866

being already present, and being highly variable, would afford the materials for adaptation to the most different purposes; and they would generally retain through the force 1869

being already present in considerable numbers, and being highly variable, would naturally afford the materials for adaptation to the most different purposes; yet they would generally retain, through the force 1872

→ inheritance. 1859 1860 1861 1866

inheritance plain traces of their original or fundamental resemblance. 1869

inheritance, plain traces of their original or fundamental resemblance. 1872

↑ 2 blocks not present in 1859 1860 1861 1866 1869; present in 1872

They would retain this resemblance all the more, as the variations, which afforded the basis for their subsequent modification through natural selection, would tend from the first to be similar; the parts being at an early stage of growth alike, and being subjected to nearly the same conditions. Such parts, whether more or less modified, unless their common origin became wholly obscure, would be serially homologous.

→ we can homologise 1859 1860 1866

we can homo- logise 1861

it can easily be shown that 1869

OMIT 1872

→ of one species with those of another and 1859

of one species with those of other and 1860 1861 1866

in 1869 1872

→ we can indicate but 1859 1860 1861 1866

are homologous, but 1869

can be shown to be homologous, only a 1872

→ that 1859 1860 1861 1866

can be indicated; that 1869

such as the valves of Chitons, can be indicated; that 1872

↑ 6 blocks not present in 1859 1860 1861 1866 1869; present in 1872

But morphology is a much more complex subject than it at first appears, as has lately been well shown in a remarkable paper by Mr. E. Ray Lankester, who has drawn an important distinction between certain classes of cases which have all been equally ranked by naturalists as homologous. He proposes to call the structures which resemble each other in distinct animals, owing to their descent from a common progenitor with subsequent modification, homogenous; and the resemblances which cannot thus be accounted for, he proposes to call homoplastic . For instance, he believes that the hearts of birds and mammals are as a whole homogenous,— that is, have been derived from a common progenitor; but that the four cavities of the heart in the two classes are homoplastic,— that is, have been independently developed. Mr. Lankester also adduces the close resemblance of the parts on the right and left sides of the body, and in the successive segments of the same individual animal; and here we have parts commonly called homologous, which bear no relation to the descent of distinct species from a common progenitor. Homoplastic structures are the same with those which I have classed, though in a very imperfect manner, as analogous modifications or resemblances. Their formation may be attributed in part to distinct organisms, or to distinct parts of the same organism, having varied in an analogous manner; and in part to similar modifications, having been preserved for the same general purpose or function,— of which many instances have been given.

→ but 1859 1860 1861

in their present state, but 1866

as they now exist, but 1869 1872

→ element. 1859 1860 1861

and simpler element. 1866 1869 1872

→ a modification of this nature having 1859 1860 1861

such modifications having actually 1866

this having 1869 1872

→ On my view these terms 1859 1860 1861 1866

According to the views here maintained, such language 1869 1872

→And as the whole amount of modification will have been effected by slight successive steps, we need not wonder at discovering in such

parts,

parts

→or organs, a certain degree of fundamental resemblance, retained by the strong principle of →inheritance. ↑

In the great class of molluscs, though →we can homologise the parts →of one species with those of another and distinct

species

species,

→we can indicate but few serial

homologies

homologies,

homologies;

→that is, we are seldom enabled to say that one part

~~or organ~~

or organ

is homologous with another

part in

the same individual. And we can understand this fact; for in molluscs, even in the lowest members of the class, we do not find nearly so much indefinite repetition of any one

part

part,

as we find in the other great classes of the animal and vegetable kingdoms. ↑

Naturalists frequently speak of the skull as formed of metamorphosed

vertebræ;

vertebræ:

the jaws of crabs as metamorphosed legs; the stamens and pistils

flowers as metamorphosed leaves; but it would in

most

these

cases

~~probably~~

probably

be more correct, as Professor Huxley has remarked, to speak of both skull and vertebræ,

~~both~~

both

jaws and legs,

&c.,

&c.,—

as having been metamorphosed, not one from the

other

other,

→but from some common →element.

Most naturalists,

Naturalists,

however, use such language only in a metaphorical

sense;

sense:

they are far from meaning that during a long course of descent, primordial organs of any kind— vertebræ in the one case and legs in the other— have actually been

converted

modified

into skulls or jaws. Yet so strong is the appearance of →a modification of this nature having occurred, that naturalists can hardly avoid employing language having this plain signification. →On my view these terms