GENERAL REVIEW OF LIVING BEINGS. 
17 
This physiological arrangement is ably illustrated by the cxcelbrnt Dr Palcy. The 
regularity of the animal structure,” ho observes, “ is rendered remarkable by the three 
following considerations : — First, the limbs, separately Lakeu, have nitt this co-rclation 
ef parts, but the contrary of it. A knife taken down the chine, cuts the human body 
into two parts, externally equal and alike ; you cannot draw a straight line which will 
not divide a hand, a foot, tho log, the thigh, the check, tho eye, the ear, into two parts 
equal and alike. Those parts which are placed upon tlie middle or partition lino of tho 
body, or which traverse that line, as the nose, the tongue, the lips, may be so divuled, 
or, more properly speaking, arc double organs ; but other parts cannot. This shows 
that the correspondency which wo have been dcsmbbig does not arise by any neces- 
sity in tho iiaturo of the subject; for, if ncces.sary, it would be universal; whereas, 
it is observed only in the system or assemblage : it is not Iruc of the separate parts ; 
tliat is to say, it is found where it conduces to beauty or utility ; it is not found wliero 
it w’ould subsist at the expense nf both. The two wings of a bird always corres- 
pond ; tho two .sides of a feather frequently do not. Iii centipedes, millepedes, and 
tlic whole tribe of InsecU, no two legs on the same side ar(? alike ; yet tlicro is the 
most exact parity between the legs opposite to one another. The next circumstance 
to be remarked is, that, whilst the cavities of the body are so configurated as exter^ 
nally to exhibit the most exact correspondency of the opposite sides, the contents of 
these cavities have no such correspondency. A line drawn down tho middle of the 
breast, divides the thorax into two sides exactly similar; yet these two sides enclose 
very different contents. The liciirt lies on tho left side, a lobe of tho lungs on the 
right, biilanoing each other neillier in size nor shape. The same thing holds of the 
abdomen. The liver lies on tho right side, without any similar riscus opposed to it 
on the left. Tlie spleen indeed is situate over against the liver, but agreeing with 
the liver neilher in bulk nor form. There is no equi-pollcncy between these. Tho 
stomach is a vessel both irregular in its shape and oblique in its position. Tho fold- 
ings and doublings of the intestines do not present a parity of sides. Yet that sym- 
metry which depends upon the co-relalion of the sides, is externally preserved through- 
out the whole trunk ; and is the more rcmai’kablc in the lower part of it, as the in- 
teguments are soft ; and the shape, consequently, is not, as tho thorax is by its ribs, 
reduced by natural stays. It is evident, therefore, that the external proportion docs 
not arise from any equality in the shape or pressure of tho internal contents. What 
is it indeed but a correction of inequalities? — an adjustment, by mutual compensation, 
of anoinaloiM forms into a regular congeries ? — the effect, in a word, of artful, and, if we 
might be permitted so to speak, of studied collocation ? Similar also to this, is a third 
observation ; that an internal inequality in the feeding vessels is so managed, as to 
produce no inequality of parts which were intended to correspond. The right arm 
answers accurately to tho left, both in size and shape ; but the arterial branches, 
which supply the two arms, do not go off* from their trunk, in a pair, in the same man- 
ner, at the same place, or at the same angle, under which want of sirailiUide it is 
very difficult to conceive how the same quantity of Wood should be pushed through 
each artery : yet the result is right ; — in tho two limbs which are nourished by 
them, we perceive no diiferenee of supply, no effects of excess or deficiency. Con- 
cerning the difference of manner, in which tho subclavian and carotid arteries, upon 
the different sides of tho Iwdy, separate themselves from the aorta, Chcseldcn seems 
to have thought, that the adv'antago which the left gains by going off* at an angle 
much more acute than tho r'lght, is made up to the right, by their going off* together 
in one branch. It is very possible that this may be tho compensating contrivance ; 
*iid if it be so, bow curious — how hydrostatlcal I” 
Many animals form .singular ami remarkable exceptions to tins general law of sym- 
metry. The Mollusca have generally their digestive orifices, as well as the distinc- 
tive characters of sex, placed on one side of the body, and that is usually the right 
side. Flat fishes swim on one side; both Iheir oyes arc placed on that which is turn- 
o<l upperr.*;o.st, and this again is almost always tho right side. Even in those animals 
which are most beautifully arranged, one side of the entire body surpasses the other 
in strength, energy, and activity, and this stronger half of the body is almost always 
the riglit side. Wc can observe this circumstance among the Crustacea; we see it 
in the side-walk of the Crab; and remarkably so in tlie Fnguru.s BemhaiHlus, or Her- 
mit Crab, where the right forcep.s is larger than the left. We even see it in tho 
larger birds, and the feathers of tho riglit wing arc always stronger mid of a better 
quality than those of tho left. 1'hc same inequality enn ho traced among the Mam- 
malia, and in none of them more so than in Man, who is, perhaps, less anibi-dextrous 
than any other animal. \Vit.h him the superiority of the right hand over the left is 
•mt altogetlier tho effect of habit, Imt is founded in iialiiro. In walking, it is the right 
and foot that give the greater impulse to the body; in hopping or leaping, every 
schoolboy, who is not naturally left-handed, n.scs his right leg in preference to the left. 
Diseases of the right are more acute than those of the left side. When a person 
wishes to examine an object most minutely, he looks at it with one eye, and that is 
almost always the right eye. Whether it be not a consequence of that more general 
law, tliat a concentration of vital force in one organ is followed by a diminution of 
'^’gour in others adjacent to it, and that tho presence of the heart at the left side de- 
prives that entire division of tho body of Iho vigour enjoyed by the right side, we shall 
at present venture to determine. 
0 liave now shown that one general plan can bo traced throughout the whole of 
Idving Beings ; that analogies, sufficiently precise, may be observed, throughout tho 
•Animal and Vegetable Kingdoms ; and that in every portion of created existence, we 
find a degree of unity and perfection, a mutual dependeneo among their parts, and the 
most exquisite symmetry in their forms. Wc shall now proceed to trace the analogy 
perceptible In the essential functions of all these beings. Whether wc examine 
^ho arrangements for the continuation of the several species, the manner in which 
*hi\t constant ingress and egress of particles, ctmstituting nutriLitjii, is fulfilled, the 
^mporaturo belonging to cacli class of beings, or that necessity which compels 
«vory one of thorn to come in immediate contact with pure air, tho results arc the 
•^me for all. It is only tlie details in the workmanship of tho great artificer that vary, 
l*ut the same divine hand is perceptible throughout the whole. Tlius, nil hiving Beings 
**<'ffuirc nutriment, hut animals alone receive the food into central cavities, and digest 
To all Living Beings air is equally essential-— all absorb it and respire; but the in- 
struments of respiration arc infinitely diversified in the several classes of living beings. 
Man and other Mammalia, Birds, and Reptiles, breathe through lungs ; the Fishes, 
on the contrary, the Crustacea, and the Mollusca, respire through gills or branchije. 
Insects, again, perform this function through trachere, or minute holes, with which 
their surfaces arc perforated ; while many Worms and Polypi appear only to absorb 
air through the pores of their skin, with which they arc every where covered. Plants 
breathe through their leaves ; and many of thmn, deprived even of leaves, only perform 
this function through the pores of the epidermis which covers their subsUince. 
Again, in respect to the arrangements for continuing the several species, we observe 
the same general design, while tho means are ever various. How different do wc see 
this function in the Mammalia — those viviparous animals, where the young, already 
active and nearly perfect, hmneiUately commence, from the moment of their separa- 
tion from tho parent, those instincts and actions, which can be terminated only by 
death ; in the numerous class of oviparous, and in the ovo-viviparous animals 1 Again, 
how iromensc the chasm between all these animals just alluded to, and the lower beings 
which are destitute of any distinctions of sex! — how difl*ercnt is the function performed 
by tho Polypi, witliont sexes, without germs, producing their kind only by buds or 
ofi*-9ets I — and then, again, another mighty chasm between these and plants, continu- 
ing their species by hermaphrodite flowers, or else by flowers of distinct sexes! Nor 
even here does variety cease to exist, for many are cryptogamous, or apparently desti- 
tute of any means for continuing their species, except by cei-tain minute and almost 
evanescent sporules or reproductive corpuscles. 
In all functions wc trace this analogy in the end, and diversity in the means ; and 
nowhere in a greater degree than in the functions peculiar to animals. Thev all 
appear to feel, yet many possess no other organ of sensation than tho skin. In very 
many we find no brain, and in others not es’cn can a vestige of nerves be traced. Il; 
is evident that they all move spontaneously, yet in many wo can find no visible marks 
of muscles or organs of motion. Wo shall, however, not enlarge at present much 
further on this point, which will be illustrated hereafter in every page of The Ani- 
mal Kingdom, but merely allude to the analogy observable among the Vertebrated 
Animals. 
The analogy among tho functions and organs of these animals is so remarkable, and 
the attention which has in consequence been paid to tliem so great, that we arc 
exceedingly apt to form limited and erroneous views of the other pju-ts of the animal 
world ; — we expect to find in the lower animals the same parts, the same functions, 
whicli are plainly observable in them. Deeply impressed with their structure and 
functions, wc can scarcely bring ourselves to imagine any living being without 
circulating fluids, a heart, blood, or vessels. So prejudiced are wc in favour of tho 
arrangements observable in the higher animals, that we can scarcely imagine any sen- 
sitive being without nerves, or any creature capable of moving without muscles. 
Tournefort even admitted plants to have muscles; nay, further, he actually described 
them. At the present day, there is little probability of our falling into a similar 
error; yet wcaro all naturally disposed, on ob:<crring a great analogy in tho functions 
of all animals, to suppose them to be identical in their structure. 
We have said that the analogy among the Vertebrated Animals is very remarkable. 
They are all possessed of a sqmial column, composed of numerous vertebra?. Within 
this solid column is lodged the spinal marrow, and it carries at one extremity a well- 
defended bony case or head, which contains the brain. In all these beings we find a 
heai'k, red blood, lungs, or gills ; in all, the organs of the five .senses are seen in greater 
or less degrees of perfection : wo find nerves, muscles, a digestive canal, more or less 
coinplitRitcd, a liver and pancreas, with evident arrangements for continuing the spe- 
cie*. With the exception perhaps of one species, they all have their mouths dis- 
posed horizontally ; and when ihey liave limbs, these are always four in number. 
This similarity prevails throughout their stimcture and functions. It is true that 
their surfaces vary remarkably according to their several destinations, while tho 
organs of motion differ greatly as they may be designed for swimming, flying, or 
walking. 'Die organs of respiration vary according as they are intended to breathe in 
water or in tbo air. But these differences in external arr.ingeraent do not prevent us 
from tracing the most exact analogy among them all. If we take all the organs, 
one by one, and compare them separately in any two vertebrated animals, we shall 
find the most exact equivalents in the two beings ; the analogy will he found perfect 
in all the essential circumstances; it is only the details which arc observed to differ. 
'J’he fish at first sight appears to have neither neck nor thorax: but on inspecting it 
more attentively, wo find it to be possessed of all the serie-sof vertebra: ; and that tlie 
different pieces of its thorax arc concentrated near the cranium, with which they are 
almost confounded. IlL Gcoffroy bat illustrated this curious organization of the Fishes 
in a philosophical and truly interesting manner. There is, however, one very re- 
markable distinction between these aquatic vertobrata and the aerial vertehrata, in 
the organs of voice, of whicli the former are completely deprived. 
The principles, wliicb must form the bases of a natural system of cla.ssification, have 
been already explained. A knowledge of internal organization, with tho laws of the 
subordination and co-oxistcncc of functions, will alone lead us to this result. 
Every function presupposes another function. Thus, when we sec a being appa- 
rently moving voluntarily w’hen irritated by any stimulant, wn infer that it feels. We, 
therefore, conclude that voluntary motion presupposes sensation. Again, Life is tem- 
porary in its action; it therefore presupposes the reproduction of individuals with the 
extinction, and perhaps also the creation, of new species. Wc also conclude that 
circulation presupposes re.spiration; because, wherever we find a heart, w'e also meet 
with lungs, just in the same mimner as we invariably find nerves whei*ever wc can dis- 
cover muscles. In fact, Life is hut an aggregation of pheiioraena produced by organs 
connected and governed by these law.s of co-existence. 
But in forming a system of classification, the difficulty consists in detecting tho 
law of subordination existing among the various combinations of these instruments 
of Life. Reflection upon the final causo or design of the fune.tions ivill often lead us 
to detect these laws ; but there are innumerable relations which no discernment could 
detect, without the nicest dissection of the bodies, or the most arduous observation 
of the habits of the animals when in their native elements. The anatomist in his 
laboratory, and the “ out-of-door ” Naturalist, who haunts the wilds of Nature, 
