admit a group to be natural which does not form a circle more or less
complete. How far the central group of M. Fries will agree with
this definition, I am not botanist enough to determine; but the normal
group of Mr. Macleay unquestionably does not, since he himself tells
us that it forms not one circle but two *. The first division, therefore,
of every group into two, although useful perhaps in some respects, is
clearly artificial.
The aberrant group, as being that which more immediately connects
one circle to another, comprehends, from necessity, a greater variety
of forms than are generally to be met with in the two others. The
union of all these aberrant forms into a circle of their own, is a
principle of natural arrangement which has hitherto been undiscovered,
and which has therefore claimed, in the following pages, most
particular attention. This union, however, must be kept perfectly
distinct from that property which Was long ago suspected to exist in
opposite points of a circle, and of which instances have been given f.
These examples, illustrating Mr. Macleay’s meaning, appear to me, as
they do to him, mere relations of analogy; since, if the suspicion of
their affinity had been just, we should have had a union of one typical
and two aberrant groups; a mode of combination which, to me at
least, Nature has in no instance exhibited.
As to the relative rank of the three primary divisions, some difference
of opinion may arise; for the truth is, that the principles by
which the value of zoological groups are regulated have not been
sufficiently investigated. Two groups may be of equal rank, and still
be vastly disproportionate in their contents. No one, for instance,
would think of pronouncing the class of birds a superior group
to that of quadrupeds, merely because the contents of the first, in
comparison to the second, are as six to one. Number cannot decide
the question; and therefore, as natural groups like these may be
equivalent in rank without being so in extent, we are left no other
* “ M. Fries lays it down as a rule, that he admits no groups whatever to be natural unless they
form circles more or less complete. Let us. then apply this rule to what he terms his central group,
and which he makes always to consist of two. Does this form a circle? If not, the group cannot be
natural according to his own definition.”—Macleay On certain general Laws, &c. Linn. Trans., xiv. 58.
ON THE NATURAL SYSTEM. if
alternative than to consider the primary circles of every group as
equal in rank and value.
But I wish not to attach too much importance to a term, or, in
drawing up these tables of affinities, to depart more than is necessary
from the usual mode of exhibiting circular groups. I have, therefore,
in every instance, detailed the subordinate divisions of the aberrant
groups, although, without this explanation, such a plan might convey
an erroneous impression of their relative value.
I must now advert to another, and, in my estimation, an unquestionable
property of natural arrangement: this is, the direct union
of typical groups, without the intervention of those which are aberrant.
A vague suspicion of something like this first occurred to me
when studying the affinities of the Laniadce, in the year 1824 *. This
property, however, belongs but to very few groups, since it has only
been detected in such as are pre-eminently abundant in species, and
are not of a higher rank than families. Beyond such groups, the
higher we ascend, the more dissimilar are the typical groups in approximating
circles; until, in looking to a diagram of the vertebrated
animals, (such, for instance, as that in the HormEnt., p. 318,) not only
does all appearance of affinity between the external or typical divisions
vanish, but it becomes even difficult, in some instances, to trace their
analogy. These inferior typical groups, indeed, may be said to have
three distinct relations of affinity: one to that which precedes i t ;
another to that by which it is followed ; and a third which unites it
to a group out of its own proper circle. The two first, on this account,
may be termed internal; the latter, external. This, however, is a
question so abstruse, and requires such nicety of investigation, that, for
the present, I should rather, perhaps, put it as a query, than consider
it as a demonstrated fact. At the same time, I must confess my utter
inability to reconcile, by any other theory, the evident and universally
acknowledged affinity between the ThamnophAlinte and the Myothe-
rinte ; between the Merulince and the Philomelina ; and more especially
between the typical Setophagce and the typical Sylvicolte.
* Zool. Journ., i. p. 302.
S 2