e to believe with our
forefathers that the earth's surface has always existed as it now
exists. For the science of geology has proved to demonstration that seas
and lands are perpetually undergoing gradual changes of relative
positions--continents and oceans supplanting each other in the course of
ages, mountain-chains being slowly uplifted, again as slowly denuded,
and so forth. Moreover, and as a closer analogy, within the limits of
animate nature we know it is the universal law that every individual
life undergoes a process of gradual development; and that breeds, races,
or strains, may be brought into existence by the intentional use of
natural processes--the results bearing an unmistakeable resemblance to
what we know as natural species. Again, even in the case of natural
species themselves, there are two considerations which present enormous
force from an antecedent point of view. The first is that organic forms
are only then recognised as species when intermediate forms are absent.
If the intermediate forms are actually living, or admit of being found
in the fossil state, naturalists forthwith regard the whole series as
varieties, and name all the members of it as belonging to the same
species. Consequently it becomes obvious that naturalists, in their work
of naming species, may only have been marking out the cases where
intermediate or connecting forms have been lost to observation. For
example, here we have a diagram representing a very unusually complete
series of fossil shells, which within the last few years has been
unearthed from the Tertiary lake basins of Slavonia. Before the series
was completed, some six or eight of the then disconnected forms were
described as distinct species; but as soon as the connecting forms were
found--showing a progressive modification from the older to the newer
beds,--the whole were included as varieties of one species.

[Illustration: FIG. 1.--Successive forms of Paludina, from the
Tertiary deposits of Slavonia (after Neumayr).]

Of course, other cases of the same kind might be adduced, and therefore,
as just remarked, in their work of naming species naturalists may only
have been marking out the cases where intermediate forms have been lost
to observation. And this possibility becomes little less than a
certainty when we note the next consideration which I have to adduce,
namely, that in all their systematic divisions of plants and animals in
groups higher than sp