Any number of instances could be
given of the varying importance for classification of the same important
organ within the same group of beings.
Again, no one will say that rudimentary or atrophied organs are of high
physiological or vital importance; yet, undoubtedly, organs in this
condition are often of much value in classification. No one will dispute
that the rudimentary teeth in the upper jaws of young ruminants, and
certain rudimentary bones of the leg, are highly serviceable in exhibiting
the close affinity between Ruminants and Pachyderms. Robert Brown has
strongly insisted on the fact that the position of the rudimentary florets
is of the highest importance in the classification of the Grasses.
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 lower jaw in Marsupials--the manner in which the wings of insects
are folded--mere colour in certain Algae--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 would have been
considered by naturalists as an important aid in determining the degree of
affinity of this strange creature to birds.
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