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Numerous instances could be given of characters derived from parts which must be considered of very trifling physiological importance, but which are universally admitted as highly serviceable in the definition of whole groups. For instance, whether or not there is an open passage from the nostrils to the mouth, the only character, according to Owen, which absolutely distinguishes fishes and reptiles— the inflection of the angle of the
in Marsupials— the manner in which the wings of insects are folded— mere colour in certain Algæ— mere pubescence on parts of the flower in grasses— the nature of the dermal covering, as hair or feathers, in the Vertebrata. If the Ornithorhynchus had been covered with feathers instead of hair, this external and trifling character
have been considered by naturalists as
→an important aid
in determining the degree of affinity of this strange creature to
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| The importance, for classification, of trifling characters, mainly depends on their being correlated with
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
and of almost universal prevalence, and yet leave us in no doubt where it should be ranked. Hence, also, it has been
that a classification founded on any single character, however important that may be, has always failed; for no part of the organisation is
constant. The importance of an aggregate of characters, even when none are important, alone
→the aphorism enunciated by Linnæus, namely,
that the characters do not give the genus, but the genus gives the characters; for this
seems founded on
appreciation of many trifling points of resemblance, too slight to be defined. Certain plants, belonging to the Malpighiaceæ, 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."
Aspicarpa produced in France, during several years, only
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 amongst the Malpighiaceæ. This case
→well
the spirit
our
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