The
intermediate species, also (and this is a very important
consideration), which connected the original species (A) and (I), have
all become, excepting (F), extinct, and have left no descendants.
Hence the six new species descended from (I), and the eight descended
from (A), will have to be ranked as very distinct genera, or even as
distinct sub-families.
Thus it is, as I believe, that two or more genera are produced by
descent, with modification, from two or more species of the same
genus. And the two or more parent-species are supposed to have
descended from some one species of an earlier genus. In our diagram,
this is indicated by the broken lines, beneath the capital letters,
converging in sub-branches downwards towards a single point; this
point representing a single species, the supposed single parent of our
several new sub-genera and genera.
It is worth while to reflect for a moment on the character of the new
species F14, which is supposed not to have diverged much in character,
but to have retained the form of (F), either unaltered or altered only
in a slight degree. In this case, its affinities to the other fourteen
new species will be of a curious and circuitous nature. Having
descended from a form which stood between the two parent-species (A)
and (I), now supposed to be extinct and unknown, it will be in some
degree intermediate in character between the two groups descended from
these species.
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