116 
SYSTEM OF NATURE. 
respectively the influence of air, earth and water, may be 
called the aerial radius, the terrestrial radius, and the aqua¬ 
tic radius. 
In addition to these three radii, whose influence is due 
to certain combinations of matter wholly independent of, 
and quite exterior to, the animal kingdom, there appear to 
be other three, whose influence is less strongly marked, 
whose distinguishing characteristics seem much more diffi¬ 
cult to define, and whose attributes are entirely animal, and 
therefore perfectly distinct from any to which names, hav¬ 
ing reference to combinations of matter apart from animal 
life, could with propriety be applied. These appear to 
alternate with the others, and the names which I propose 
applying to them are these ; — saltant, ambulant and 
rapacious. 
These animal radii are connected with the concentric 
radii in pairs, thus the aerial and saltant; the terrestrial 
and ambulant; the aquatic and rapacious. The pairs of 
groups to which their influence extends are already no¬ 
ticed, and will again be brought under review. 
It has been said that the concentric circles indicate de¬ 
grees of structure : together they form a graduated scale 
of which man is the summit: in estimating the position of 
any group on this scale, the terms superior and inferior are 
liable to misapplication : the grade to which any animal is 
entitled must not depend on our opinion of its perfection 
or imperfection, but on its approach to, or departure from, 
the normal form of man. The radii, on the contrary, are the 
indices to economy. On the correct appreciation of these 
characters — structure and economy—depends the whole 
secret of natural classification. From overlooking or un¬ 
dervaluing these distinct sources of difference, and thus 
