upports his theory, not by scientific, but by metaphysical evidence;
his theory is "essentially and completely metaphysical in character,
resting altogether upon that idea of 'the infinite' which the human
mind can neither put aside nor comprehend."[10] And so a theory which
will be generally objected to as much too physical is transposed by a
single syllogism to metaphysics.

Well, physical geology must go with it: for, even on the soberest
view, it demands an indefinitely long time antecedent to the
introduction of organic life upon our earth. _A fortiori_ is physical
astronomy a branch of metaphysics, demanding, as it does, still larger
"instalments of infinity," as the reviewer calls them, both as to time
and number. Moreover, far the greater part of physical inquiries now
relate to molecular actions, which, a distinguished natural
philosopher informs us, "we have to regard as the results of an
infinite number of infinitely small material particles, acting on each
other at infinitely small distances,"--a triad of infinites,--and so
_physics_ becomes the most _metaphysical_ of sciences.

Verily, on this view,

"Thinking is but an idle waste of thought,
And nought is everything, and everything is
nought."

The leading objection of Mr. Agassiz is likewise of a philosophical
character. It is, that species exist only "as categories of
thought,"--that, having no material existence, they can have had no
material variation, and no material community of origin. Here the
predication is of species in the subjective sense, while the inference
is applied to them in the objective sense. Reduced to plain terms, the
argument seems to be: Species are ideas; therefore the objects from
which the idea is derived cannot vary or blend, cannot have had a
genealogical connection.

The common view of species is, that, although they are
generalizations, yet they have a direct objective ground in Nature,
which genera, orders, etc., have not. According to the succinct
definition of Jussieu,--and that of Linnaeus is identical in
meaning,--a species is the perennial succession of similar individuals
in continued generations. The species is the chain of which the
individuals are the links. The sum of the genealogically connected
similar individuals constitutes the species, which thus has an
actuality and ground of distinction not shared by genera and other
groups which were not supposed to be genealogically connected. How a
derivati