egetable kingdoms, there are certain forms which I termed PERSISTENT
TYPES, which have remained, with but very little apparent change, from
their first appearance to the present time.

6. In answer to the question "What, then, does an impartial survey of the
positively ascertained truths of palaeontology testify in relation to the
common doctrines of progressive modification, which suppose that
modification to have taken place by a necessary progress from more to
less embryonic forms, from more to less generalised types, within the
limits of the period represented by the fossiliferous rocks?" I reply,
"It negatives these doctrines; for it either shows us no evidence of such
modification, or demonstrates such modification as has occurred to have
been very slight; and, as to the nature of that modification, it yields
no evidence whatsoever that the earlier members of any long-continued
group were more generalised in structure than the later ones."

I think that I cannot employ my last opportunity of addressing you,
officially, more properly--I may say more dutifully--than in revising
these old judgments with such help as further knowledge and reflection,
and an extreme desire to get at the truth, may afford me.

1. With respect to the first proposition, I may remark that whatever may
be the case among the physical geologists, catastrophic palaeontologists
are practically extinct. It is now no part of recognised geological
doctrine that the species of one formation all died out and were replaced
by a brand-new set in the next formation. On the contrary, it is
generally, if not universally, agreed that the succession of life has
been the result of a slow and gradual replacement of species by species;
and that all appearances of abruptness of change are due to breaks in the
series of deposits, or other changes in physical conditions. The
continuity of living forms has been unbroken from the earliest times to
the present day.

2, 3. The use of the word "homotaxis" instead of "synchronism" has not,
so far as I know, found much favour in the eyes of geologists. I hope,
therefore, that it is a love for scientific caution, and not mere
personal affection for a bantling of my own, which leads me still to
think that the change of phrase is of importance, and that the sooner it
is made, the sooner shall we get rid of a number of pitfalls which beset
the reasoner upon the facts and theories of geology.

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