122 
SYSTEM OF NATURE. 
pairs so far apart, that they always crawl on their bellies 
in the same manner as snakes; the armadilloes and ant- 
eaters are the third grade or step, and in them the reptile 
gait is still preserved, although perhaps less conspicuously; 
to the gait and economy of the fourth group, the giant fos¬ 
sil sloths, we have but a slender guide in the scattered rem¬ 
nants now in existence. 
The distinguishing characters of the ambulant radius, 
like those of the saltant, are difficult to define with preci¬ 
sion ; and I trust to the intelligence of zoologists in tracing 
the peculiarities, all unimportant though they may seem, 
which obviously distinguish it, rather than resort to others 
which might require hypothesis to support them. These 
obvious characters are lethargy, sloth, vegetable food, in¬ 
sensibility to pain, tenacity of life, thickness of covering, 
and others nearly analogous. The series commences with 
the shell-bearing mollusks, then goes on to the tortoises, 
then to the Belluae, and lastly to the sloths. 
The aquatic radius ascends through the province Zoo- 
phyta, the class Pisces Ossei, the tribe Cete, and is sup¬ 
posed to enter the Primates by means of some aquatic 
animal at present unknown. Its companion radius, the 
rapacious, ascends through the province Radiata, the class 
Pisces Cartilaginei, the tribe Ferae, and the order or family 
of Cebidae or American monkeys. In this instance the 
characters of both rays are perfectly defined, perhaps even 
more strikingly than in the preceding instances, until we 
enter the Primates, where they appear lost. Surely it is 
unnecessary to dwell on characters so obvious: if the aqua¬ 
tic character be not evident on the mere mention of zoo¬ 
phytes, fishes and whales, it cannot be enforced by any 
arguments of mine. 
