the parts
of one species with those of other and | of one species with those of other and 1860 1861 1866 |
| of one species with those of another and 1859 |
| in 1869 1872 |
| species, 1859 1860 1861 1866 | | species 1869 1872 |
| we can indicate but 1859 1860 1861 1866 |
| are homologous, but 1869 |
| can be shown to be homologous, only a 1872 |
| homologies; 1859 1860 1861 1866 | | homologies 1869 | | homologies, 1872 |
| that 1859 1860 1861 1866 |
| can be indicated; that 1869 |
| such as the valves of Chitons, can be indicated; that 1872 |
| or organ 1859 1860 1861 1866 | or organ 1869 1872 |
| in 1859 1860 1861 1866 | | part in 1869 1872 |
| part, 1859 1860 1861 1866 1869 | | part 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.
|
|
|
Naturalists frequently speak of the skull as formed of metamorphosed
vertebræ: | vertebræ: 1859 1860 1861 1866 | | vertebræ; 1869 1872 |
| of 1859 1860 1861 1866 | | in 1869 1872 |
| these 1859 1860 1861 1866 | | most 1869 1872 |
| probably 1859 1860 1861 1866 1869 | probably 1872 |
| both 1859 1860 1861 1866 1869 | both 1872 |
| &c.,— 1859 1860 1861 | | &c., 1866 1869 1872 |
| other, 1859 1860 1861 1869 1872 | | other 1866 |
| 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 |
| Naturalists, 1859 1860 1861 | | Most naturalists, 1866 1869 1872 |
| sense: 1859 1860 1861 1866 | | sense; 1869 1872 |
| modified 1859 1860 1861 1866 | | converted 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 |
| would probably 1859 1860 1861 | | probably would 1866 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.
|
|
|
Embryology
.—
|
It has already been
casually remarked that certain organs | 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 |
|
