ps
on account of a radiating wreath of feelers around the upper part of
their body: yet, when examined closely, this wreath is found to be
incomplete; it does not, form a circle, but leaves an open space between
the two ends, where they approach each other, so that it has a horseshoe
outline, and partakes of the bilateral symmetry characteristic of its
type and on which its own structure is based. These series have not yet
been very carefully traced, and young naturalists should turn their
attention to them, and be prepared to draw the nicest distinction
between analogies and true affinities among animals.

VIII.

After this digression, let us proceed to a careful examination of the
natural groups of animals called Families by naturalists,--a subject
already briefly alluded to in a previous chapter. Families are natural
assemblages of animals of less extent than Orders, but, like Orders,
Classes, and Branches, founded upon certain categories of structure,
which are as distinct for this kind of group as for all the other
divisions in the classification of the Animal Kingdom.

That we may understand the true meaning of these divisions, we must not
be misled by the name given by naturalists to this kind of group. Here,
as in so many other instances, a word already familiar, and that had
become, as it were, identified with the special sense in which it
had been used, has been adopted by science and has received a new
signification. When naturalists speak of Families among animals, they do
not allude to the progeny of a known stock, as we designate, in common
parlance, the children or the descendants of known parents by the word
family; they understand by Families natural groups of different kinds
of animals, having no genetic relations so far as we know, but agreeing
with one another closely enough to leave the impression of a more
or less remote common parentage. The difficulty here consists in
determining the natural limits of such groups, and in tracing the
characteristic features by which they may be defined; for individual
investigators differ greatly as to the degree of resemblance existing
between the members of many Families, and there is no kind of
group which presents greater diversity of circumscription in the
classifications of animals proposed by different naturalists than these
so-called Families.

It should be remembered, however, that, unless a sound criterion be
applied to the limitation of Familie