GENERAL REVIEW OR LIVING BEINGS. 
19 
THE ANIMAL KINGDOM. 
]. Mammalia 
2. Aves 
3. Reptilia... 
4. Pisces 
DIVISION I VERTEBRATA, SUBDIVIDED INTO FOUR CLASSES. 
f Man and Beasts, with ivarm blood; heart with two ventricles; females suckling their young with milk, secreted in breasts 
or mammas; viviparous, excepting the Monotremata, which are cither oviparous or ovo-viviparous. 
f Birds, with warm blood; heart with two ventricles; no mammae; oviparous; body covered with feathers, and orgauizei' 
\ for flight. 
f Reptiles, with cold blood; heart with one ventricle ; having lungs, or sometimes only gills or branchiae; oviparous, or 
I ovo-viviparous; generally amphibious. 
f Fishes, with cold blood; heart with one ventricle; no lungs, but breathing by branchim;. generally oviparous; bodj- or- 
^ ganized for swimming. 
DIVISION II.— MOLLUSCA, SUBDIVIDED INTO SIX CLASSES. 
F Cuttle-fishes, having the mantle furnished with a shell, and united under the body, forming a muscular sac; head con- 
1. Cephalopoda... nected with the mouth of the sac, and crowned with long and strong fleshy limbs, for walking on, and seizing their prey ; 
{ with two large eyes; and two gills placed in the sac. Sexes separate. 
2. Ptekoimda Marine animals without feet; with two fins, placed one on each side of the mouth; head distinct; hermaphrodites. 
3 Gastekopoda i Snails or Slugs, and Limpets, with a distinct head; crawling on a fleshy disc; very seldom with fins; generally with a 
^ shell ; tcntacula from two to six. 
4. Acephala ; .Aquatic animals, generally with a bivalve or multivalve shell; without an apparent head or limbs; mouth concealed bc- 
tween the folds or in the bottom of the mantle ; hermaphrodites ; branchite external ; incapable of locomotion. 
5 Brachiopoda f Marine Animals, without a head; having two fleshy arms, furnished with numerous filaments; bivalve shells; incapable 
of locomotion. 
6 CninnopoD v ^ Barnacles, inclosed in a multivalve shell ; with numerous articulated limbs or cirrhi, disposed in pairs ; incapable of loco- 
motion. General structure approaching to the articulated animals. 
1. Annelides 
2. CuUSTACEA 
3. Ae.aciinides 
4. Insecta 
DIVISION III ARTICDL.AT.4. SUBDIVIDED INTO FOUR CLASSES. 
f Worms, generally with red blood; without limbs; usually hermaphrodites, perfect or reciprocal ; bodysoft; more or less 
^ elongated, and divided into numerous segments; circulation double, with one or more hearts or fleshy ventricles ; respir- 
(^ing generally through branchim; sometimes dwelling within membraneous, horny, or calcareous tubes. 
C Marine Animals, with a crustaceous envelope, having articulated limbs attached to the sides of the body; blood w'hitc; 
always with articulated antennm or feelers hi front of the head, and generally four in number; distinct organs of circula- 
( tion ; respiring through branchiie. 
J Spiders, with the head and breast united in a single piece, and with the principal viscera situate in a distinct abdomen, 
( behind the thorax ; without antennae; oidparous. 
...Insects, divided into three distinct parts, the head, thorax, and abdomen; always with two antennm, and six feet. 
DIVISION IV RADIAT.A, SUBDIVIDED INTO FIVE CLASSES. 
1. F.CHlNODEaM.ATA 
2. Entozoa 
3. Acalepii.e 
4. PoT.TPI 
5. I.XFUSORIA 
C Sea-hedgehogs, and Sea-stars, with distinct viscera and organs of respiration; witli a partial circulation; often with a 
kind of skeleton, armed with points or moveable "spines ; destitute of head, eyes, and articulated feet; nervous system 
( indistinct ; organs of motion qxtrerncly imperfect. 
{ Intestinal Worms, with no distinct organs of circulation oi respiration; body generally elongated, and organs arranged 
longitudinally; without head, eyes, or feet. 
....Medusae, or Sea-nettles, without organs for circulation or respiration; with only one entrance to the stomach. 
{ Small Gelatinous Animals, with only one entrance to the stomach, surrounded with tentacida; generally adhering togetlicr 
and forming compound animals. 
f Animalcules, or Minute Microscopic Animals, found in fluids, or vegetable infusions. As their internal structure is but 
-( little known from their extreme smallness, this cla.ss will probably bo found hereafter to contain animals which ought to 
f be placed in some of the higlicr divisions. 
sect. XI. — GENERAL REVIEW OE LIVING BEINGS CONTINUED. 
^vhordinaiion of Chaructera — hnaginary Chain of Beings — Circular Tlijpothcses. 
luE preceding Tables exhibit the primary and secondary division.s of Living Beings, 
hi the course of this work, wo shall describe the organs and functions from which their 
characters are derived. At present let us consider somewhat further the laws of their 
*abordination and eo-existenco. 
Upon investigating the internal structure of the entire Animal Kingdom, certain 
heings are discovered, consisting of a stomach isolated from every other organ, without 
'isible nerves or muscles, without a heart or vessels, and destitute of a brain and organs 
nf sense. We are, therefore, led to consider the stomach as the most essential cha- 
tecter. The most variahlo oi’gans must be regarded as of the least importance; and 
"10 thence eeuclude that the nerves, muscles, heart, lungs, and brain, are subordinate 
characters. 
But on investigating the more complex animals provided with .all the organs just 
'numerated, and upon studying the gradual progress of their development, it is found 
hiat the heart is the first formed of the organs, or at least it is the first visible organ, 
*ih 1 that one in which the vital action is most evident. Upon examining the structure 
“f monstrooa heings, we obs(nwo that the heart can exist without the other organs 
Blurb oftener and more perfectly than they car. exist without the heart. Again, wlicn 
me observe an animil alrc.ady brought to light, and increased in magnitude, we see the 
eigans of sense, the brain, and the greater number of muscles, suspend their functions 
a periodical sleep; wo see the lungs themselves sometimes cease to act for a short 
•face of time; while the heart continues to beat as long as life exists. For all these 
reasons, the heart appears to be the most important organ among the higher ani- 
miils. 
It must be admitted, however, that many difficulties prevent us from determining 
precisely which of the five organs, essential to the life of a vortebrated animal, is the 
most important, when we see the animal healthy, full grown, perfectly formed, eaclx 
organ exactly performing all its functions, juid the entire being in the full exercise of 
all its powers. It has been already explained that the whole of the organs pre.suppose 
a stomach which nourishes them. The lungs and gills cannot exist without the brain ; 
the brain in its turn requires the action of the heart; and the heart itself cannot per- 
form its functions without the aid of the spinal marrow and of tho lungs, which are 
ruled by tho brain. All tho organs form a mutually-counccling bond of union. It is 
true that if we examine in detail any one of the subordinate organs, it nppear.s to 
have more need of tlie blood than of the nerves, and that it can exist longer without 
tho action of the brain than of the heart. But if we contemplate any part of the 
complicated whcidwork essential to Life, it is found to bo reciprocally connected, 
and this even in the most varied and intricate manner. Yet, when we see the heart 
commeneiug to beat before the stomach and lungs are in action, — when it is observed 
to throb during the absence of respiration, or after it has altogether ceased, — when 
we see that mutilations of tho brain do not always produce instantaueous death, 
while the destruction of the spinal marrow- speedily causes the heart to cease its move- 
ments, — we have suffiuient grounds for supposing that tho circulation of tlie blood is 
the primary essential condition of existence among any of the higher animals. For 
those reasons, in arranging the numerous subjects of tho Animal Kingdom, the spinal 
marrow, which appears to govern the action of the heart, must be considered us tlie 
