390 C. J. Sundevall on the Wings of Birds. 
greater value merely because it is derived from the relations 
of internal parts, of which the many exceedingly unnatural 
systematic classifications, founded upon so-called anatomical 
characters, are a clear proof*. 
Thus what is characteristic may just as easily be over¬ 
looked in the internal as in the external parts ; but, should 
it be correctly grasped, every part of an animal's surface or 
covering ought to furnish characters just as reliable for the 
animal’s affinities as the inner or so-called nobler parts; for 
the cause, predetermined in the egg, which makes an animal 
belong to one or the other class, order, family, species, &c., 
has continued to act uninterruptedly throughout the whole 
development upon every part of the animal's body, both exter¬ 
nal and internal, and has necessarily left behind some impress 
which may be distinguished from all others. But as different 
causes must produce different effects, it becomes impossible 
that any particular part in an animal can be exactly similar 
to a part in another animal of a different order, genus, &c. 
JFrom a physiological point of view, indeed, the internal parts 
may be regarded as more important than the external; but 
zoographically we must regard the external parts as possess¬ 
ing an equal if not greater value, because the characters 
derived from them can be easily recognized and examined in 
the specimens of natural products which usually occur, 
which is not the case with those founded upon the internal 
parts; and I venture to maintain that only external form- 
characters ought to be employed in zoographical diagnoses, 
and also that the external parts always present such charac¬ 
ters as express quite clearly the affinities of the species, 
although these characters may not always lie open to super¬ 
ficial observation. The wing-feathers may therefore furnish 
just as important characters as any other part of a bird's 
body, and an accurate knowledge of them may be of the 
greatest value in ornithology. 
* B. g. the classifications of the Arachnida frorp the organs of respira¬ 
tion, the divisions in the class Vermes in accordance with differences in 
the nervous system, the arrangement of the Gasteropoda according to 
the branchiae, &c. 
