SYSTEM OF NATURE. 
35 
legs also are short, whose bellies are on the ground, whose 
progress is repent or creeping, as the ant-eaters. 6thly. 
The Belluae are Ambulantia or walkers, whose legs are 
long and strong, who often look as though on stilts, as the 
giraffe. 7thly. The Cete are Natantia or swimmers, whose 
legs are changed into fins, as the dolphin. These defini¬ 
tions are avowedly deficient in precision, and are often in¬ 
applicable to a portion of the animals they are intended 
to include, but still they appear to be natural: divisions 
founded on them bear the test of rigid anatomical investi¬ 
gation, and the food and mode of life bear a close relation 
to the structure. To the technical zoologist such divisions 
appear puerile, but as he advances from the study of dry 
technicalities to the study of natural habits and economy, 
he will perceive that they are neither superficial nor arbi¬ 
trary. To the uninstructed the simplicity of such divisions 
must ever prove a recommendation, and it may be ad¬ 
vanced in favor of the parallels to which such obvious 
characters will frequently lead us, that they were, for the 
most part, pointed out by Linneus. It should, however, 
be observed with regard to parallels of this kind, that they 
only exist in an eminent and obvious degree when the 
groups furnishing the parallels are possessed of many 
structural characters in common. But this subject will 
claim further consideration when I attempt to sketch the 
divisions of birds, &c. To return to the marsupials : 
if I assign names and characters to certain divisions 
of placentals, as proposed in a very superficial manner 
above, and if the marsupials really form a distinct group 
equivalent to the placentals and birds, they ought to 
be divisible into minor groups distinguishable by some¬ 
what similar characters. It must, however, be observed, 
d 2 
