unded on few or
isolated specimens, have had their true nature determined by the study
of a good series of examples: they have been thereby established as
species or as varieties; and the number of times this has occurred is
doubtless very great. But there are other, and equally trustworthy
cases, in which, not single species, but whole groups have, by the study
of a vast accumulation of materials, been proved to have no definite
specific limits. A few of these must be adduced. In Dr. Carpenter's
"Introduction to the Study of the Foraminifera," he states that "_there
is not a single specimen of plant or animal of which the range of
variation has been studied by the collocation and comparison of so large
a number of specimens as have passed under the review of Messrs.
Williamson, Parker, Rupert Jones, and myself, in our studies of the
types of this group_;" and the result of this extended comparison of
specimens is stated to be, "_The range of variation is so great among
the Foraminifera as to include not merely those differential characters
which have been usually accounted_ SPECIFIC, _but also those upon which
the greater part of the_ GENERA _of this group have been founded, and
even in some instances those of its_ ORDERS" (Foraminifera, Preface, x).
Yet this same group had been divided by D'Orbigny and other authors into
a number of clearly defined _families_, _genera_, and _species_, which
these careful and conscientious researches have shown to have been
almost all founded on incomplete knowledge.

Professor DeCandolle has recently given the results of an extensive
review of the species of Cupuliferae. He finds that the best-known
species of oaks are those which produce most varieties and subvarieties;
that they are often surrounded by provisional species; and, with the
fullest materials at his command, two-thirds of the species he considers
more or less doubtful. His general conclusion is, that "_in botany the
lowest series of groups,_ SUBVARIETIES, VARIETIES, _and_ RACES _are very
badly limited; these can be grouped into_ SPECIES _a little less vaguely
limited, which again can be formed into sufficiently precise_ GENERA."
This general conclusion is entirely objected to by the writer of the
article in the "Natural History Review," who, however, does not deny its
applicability to the particular order under discussion, while this very
difference of opinion is another proof that difficulties in the
determination of sp