This is represented in the
diagram by the letter F14.
All the many forms, extinct and recent, descended from A, make, as
before remarked, one order; and this order, from the continued effects
of extinction and divergence of character, has become divided into
several sub-families and families, some of which are supposed to have
perished at different periods, and some to have endured to the present
day.
By looking at the diagram we can see that if many of the extinct
forms, supposed to be embedded in the successive formations, were
discovered at several points low down in the series, the three
existing families on the uppermost line would be rendered less
distinct from each other. If, for instance, the genera a1, a5, a10,
f8, m3, m6, m9 were disinterred, these three families would be so
closely linked together that they probably would have to be united
into one great family, in nearly the same manner as has occurred with
ruminants and pachyderms. Yet he who objected to call the extinct
genera, which thus linked the living genera of three families
together, intermediate in character, would be justified, as they are
intermediate, not directly, but only by a long and circuitous course
through many widely different forms. If many extinct forms were to be
discovered above one of the middle horizontal lines or geological
formations--for instance, above Number VI.--but none from beneath this
line, then only the two families on the left hand (namely, a14, etc.
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