ZOOLOGY. 
contained in water hy means of their gills. 
Amphibia receive the air into their lungs, 
but their blood is likewise cold, and in both 
fishes and amphibia the heart has only two 
regidar cavities, while that of animals with 
warm blood has four. Of the latter, the 
oviparous are birds, and are generally co- 
vered with feathers, the viviparous are ei- 
ther quadrupeds or cetaceous animals, and 
are furnished with organs for suckling their 
young. See Physiology. 
Each of the classes of animals is subdi- 
vided by Linnaeus into different orders: for 
a scientific account of these orders, and 
also of the classes from whence they spring, 
the reader is referred to the several heads 
of the Dictionary in the alphabetical order ; 
and here we shall take a cursory view of 
the subject, in order to give, in a short 
compass, a sort of outline of the science. 
The fimt cla.ss, denominated Mammalia, 
from the female’s suckling its young, com- 
prehends all viviparous animals with warm 
blood. These, with very few exceptions, 
have teeth fixed in their jaw bones ; and 
from the form and number of these teeth, 
the orders are distinguished, except that of 
cetaceous fishes, which is known by the fins 
that are found in the place of feet. The 
distinctions of the teeth are somewhat mi- 
nute, but they appear to be connected with 
the mode of life of the animal, and they 
are tolerably natural. The first order. Pri- 
mates, contains man, monkeys, and bats : 
tlje second, Bruta; among others, the ele- 
phant, the rhinoceros, the ant-eater, and 
the ornithorhynchus, an extraordinay qua- 
druped, lately discovered in New Holland, 
with a bill like a duck, and sometimes teeth 
inserted behind it; but there are some sus- 
picions that the animal is oviparous. The 
order Ferae contains the seal, the dog, the 
cat, the lion, the tiger, the weasel, and the 
mole, most of them beasts of i>rey ; the 
opossum and the kangaroo also belong to 
this order, and the kangaroo feeds on vege- 
tables, although its teeth are like those of 
carnivorous animals. The fourth order, 
Glires, comprehends beavers, mice, squir- 
rels, and hares : the fifth, Pecora, camels, 
goats, sheep, and horned cattle. The sixth 
order, Belluae, contains the horse, the hip- 
popotamus, and the hog. The cetaceous 
fishes, or whales, form the seventh and last 
order; they reside in the water, enveloped 
in a thick clothing of fat, that is, of oily 
matter, deposited in cells, which enables 
their blood to retain its temperature, not- 
withstanding the external contact of a dense 
medium considerably colder. 
Birds are distinguished from quadrupeds 
by their laying eggs ; they are also gene- 
rally feathered, although some few' are ra- 
ther hairy, and instead of hands, or fore- 
legs, tliey have wings. Their eggs are co- 
vered by a calcareous shell ; and they con- 
sist of a white, or albumen, which nou- 
rishes the chick during incubation, and a 
yolk, which is so suspended within it, as to 
preserve the side on which the little rudi- 
ment of a chicken is situated, continually 
uppermost, and next to the mother that is 
sitting on it. The yolk is, in great mea- 
sure, received into the abdomen of the 
chicken a little before the time of its being 
hatched, and serves for its support, like the 
milk of a quadruped, and like the cotyle- 
dons of young plants, until the system is 
become sufficiently strong for extracting its 
own food out of the ordinary nutriment of 
the species. 
Birds are divided, according to the form 
of their bills, into six orders: Accipitres; 
as eagles, vultures, and hawks. Pic* ; as 
crows, jackdaws, humming birds, and par- 
rots. Anseres ; as ducks, swanii, and gulls, 
Grallas; as herons, woodcocks, and os- 
triches. Gallinae ; as peacocks, pheasants, 
turkies, and common fowls. And, lastly, 
Passeres; compiehending sparrows, larks, 
swallows, thrushes, and doves. The Am- 
phibia are in some respects very nearly al- 
lied to birds: but their blood is little 
warmer than the surrounding medium. 
Their respiration is not necessarily per- 
formed in a continual succession of alter- 
nations since t,he whole of their blood does 
not pass through the lungs, and the circula- 
tion may continue without interruption in 
other parts, although it may be impeded in 
these organs, for w'ant of the motion of re- 
spiration. They are very tenacious of life ; 
it has been asserted on good authority, that 
some of Ihem have lived many years with- 
out food, inclosed in hollow trees, and even 
in the middle of stones : and they often re- 
tain vestiges of life some days after the loss 
of their hearts. Their eggs are generally 
covered with a membrane only. They 
have sometimes an intermediate stage of 
existence in which all their parts are not 
yet developed, as we observe in the tad- 
pole ; and in this respect they resemble the 
class ot insects. They are now universally 
considered as dividerl into two orders only ; 
Reptilia: as the tortoise, the dragon, or 
flying lizard, the frog, and the toad; all 
these have four feet : but the animals which 
belong to the order Serpentes are without 
feet. Most of the serpentes are perfectly 
