Origin of Species Variorum

→ of one species with those of other and 1860 1861 1866

of one species with those of another and 1859

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

→ during a long course of descent 1859 1860 1861 1866

OMIT 1869 1872

→ legs, or from some simple appendage, is 1859 1860 1861

though simple legs, is 1866

though extremely simple legs, is 1869

though extremely simple legs, is in part 1872

←Subtitle not present 1859 1860 1861 Embryology and Development . 1866 1869 1872

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

This is one of the most important departments of natural history.

→ casually remarked that certain organs 1859 1860 1861

remarked that various parts and organs of the same individual animal are during an early embryonic period exactly like each other, but become 1866

stated that various parts and organs 1869

stated that various parts 1872

→ individual, which when mature become widely different and serve for different purposes, are in the embryo exactly alike. 1859 1860 1861

adult state widely different and serve for widely different purposes. 1866

same individual are exactly like each other during an early embryonic period, but in the adult state become widely different and serve for widely different purposes. 1869

same individual which are exactly alike during an early embryonic period, become widely different and serve for widely different purposes in the adult state. 1872

the parts →of one species with those of other 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 may be used literally; and the wonderful fact of the jaws, for instance, of a crab retaining numerous characters, which they

probably would

would probably

have retained through inheritance, if they had really been metamorphosed →during a long course of descent from true →legs, or from some simple appendage, is explained. → ↑

Embryology .—

It has already been →casually remarked that certain organs in the →individual, which when mature become widely different and serve for different purposes, are in the embryo exactly alike.