110 
SYSTEM OF NATURE. 
denominated Primates. A space in the second circle is va¬ 
cant, and I have suggested the possibility of this eventu¬ 
ally being filled by an aquatic animal resembling the 
monkeys : this idea, however, not resulting from absolute 
fact, is to be considered as hypothetical, and is not em¬ 
ployed as affording any evidence in favour of the propo¬ 
sitions hereafter advanced. 
Within the third circle are the Glires or rodent animals, 
the Belluae or hoofed animals, and the Ferae or beasts of 
prey ; and within the fourth circle are the Cheiroptera or 
bats, the Bruta or ant-eaters and armadilloes, and the Cete 
or whales : these six groups, together with the Primates, 
constitute the class of Placentalia or placental animals. 
Within the fifth circle are the Marsupialia or pouched 
animals, the Cataphracta or tortoises and turtles, and per¬ 
haps also the crocodiles, and the Pisces cartilaginei or 
cartilaginous fishes; and within the sixth circle are the 
Aves or birds, the Reptilia or lizards, snakes, &c., and the 
Pisces ossei or bony fishes : these six groups, together 
with the placental animals, constitute the province of Ver- 
tebrata or vertebrated animals. 
Within the seventh circle are the Aptera of Aristotle, 
comprising the Crustacea, spiders, centipedes, &c., the 
Mollusca or molluscous animals, and the Radiata or true 
radiate animals, as starfishes, sea-urchins, Medusae, &c.; 
and within the eighth or exterior circle are the Pterota of 
Aristotle or winged insects, the Vermes Annelida or worms, 
and the Zoophyta and Amorphozoa or zoophytes and 
sponges : these together constitute that vast and diversified 
assemblage which zoologists have aptly and emphatically 
denominated invertebrate animals, and which, together with 
the Vertebrata, constitute the entire animal kingdom. 
