Vertebrata. If the Ornithorhynchus had been
covered with feathers instead of hair, this external and trifling
character would have been considered by naturalists as an important aid
in determining the degree of affinity of this strange creature to birds.

The importance, for classification, of trifling characters, mainly
depends on their being correlated with many other characters of more or
less importance. The value indeed of an aggregate of characters is very
evident in natural history. Hence, as has often been remarked, a
species may depart from its allies in several characters, both of high
physiological importance, and of almost universal prevalence, and yet
leave us in no doubt where it should be ranked. Hence, also, it has been
found that a classification founded on any single character,
however important that may be, has always failed; for no part of the
organisation is invariably constant. The importance of an aggregate of
characters, even when none are important, alone explains the aphorism
enunciated by Linnaeus, namely, that the characters do not give the
genus, but the genus gives the character; for this seems founded on the
appreciation of many trifling points of resemblance, too slight to be
defined. Certain plants, belonging to the Malpighiaceae, bear perfect
and degraded flowers; in the latter, as A. de Jussieu has remarked, "The
greater number of the characters proper to the species, to the genus,
to the family, to the class, disappear, and thus laugh at our
classification." When Aspicarpa produced in France, during several
years, only these degraded flowers, departing so wonderfully in a number
of the most important points of structure from the proper type of the
order, yet M. Richard sagaciously saw, as Jussieu observes, that this
genus should still be retained among the Malpighiaceae. This case well
illustrates the spirit of our classifications.

Practically, when naturalists are at work, they do not trouble
themselves about the physiological value of the characters which they
use in defining a group or in allocating any particular species. If they
find a character nearly uniform, and common to a great number of forms,
and not common to others, they use it as one of high value; if common to
some lesser number, they use it as of subordinate value. This principle
has been broadly confessed by some naturalists to be the true one; and
by none more clearly than by that excellent botanist, Aug. St. Hila