| → allied genera, which lived 1859 1860 1861 1866 |
| allied genera existing 1872 |
| OMIT 1869 |
|
| → and these have 1859 1860 1861 1866 |
| allied genera, 1869 |
| and 1872 |
|
| → a species which existed at an unknown anterior period. 1859 1860 1861 1866 |
| some still earlier forms. 1869 |
| some still earlier form. 1872 |
|
| → I) have 1859 1860 1861 1866 |
| I) the species have 1869 |
| I), a species has 1872 |
|
|
the mere putting together and separating objects more or less alike. |
|
| But I must explain my meaning more fully. I believe that the
arrangement
of the groups within each class, in due subordination and relation to
must be strictly genealogical in order to be natural; but that the
amount
of difference in the several branches or groups, though allied in the same degree in blood to their common progenitor, may differ greatly, being due to the different degrees of modification which they have undergone; and this is expressed by the forms being ranked under different genera, families, sections, or orders. The reader will best understand what is meant, if he will take the trouble
to the diagram in the fourth chapter. We will suppose the letters A to L to represent
→allied genera, which lived
during the Silurian
→and these have
descended from
→a species which existed at an unknown anterior period.
three of these genera (A, F, and
→I) have
transmitted modified descendants to the present day, represented by the fifteen genera
(
a
14 z
14
)
on the uppermost horizontal line. Now all these modified descendants from a single species, are
related in blood or descent
the same degree; they may metaphorically be called cousins to the same millionth degree; yet they differ widely and in different degrees from each other. The forms descended from A, now broken up into two or three families, constitute a distinct order from those descended from I, also broken up into two families. Nor can the existing species, descended from A, be ranked in the same genus with the parent A; or those from I, with the parent I. But the existing genus
F
14
may be supposed to have been but slightly modified; and it will then rank with the parent-genus F; just as
|
