GENERAL REVIEW OF LIVING BEINGS. 



17 



This physioloffical arrangement is ably illustrated by the excellent Dr Paley. *' The 

 re-'ularity of the animal structure," he observes, " is rendered remarkable by the three 

 followin" considerations : — First, the limbs, aeparately taken, have not this co-relation 

 of 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, the leg, the thigh, the check, the eye, the ear, into two parts 

 equal and alike. Those parts which are placed upon the middle or partition line of the 

 body, or which traverse that line, as the nose, the tongue, the lips, raay be so divided, 

 or, more properly speaking, are double organs; but other parts cannot. This shows 

 that the correspondency which we have been describing does not arise by any neces- 

 sity in the nature of the subject; for, if necessary, it would be universal; whereas, 

 it is observed only in the system or assemblage : it is not true of the separate parts ; 

 that is to say, it is found where it conduces to beauty or utility ; it is not found where 

 it would subsist at the expense of both. The two wings of a bird ahvays corres- 

 pond ; the two sides of a feather frequently do not. In centipedes, millepedes, and 

 the whole tribe of Insects, no two logs on the same side are alike ; yet there is the 

 most exact parity between the legs opposite to one another. The nest circumstance 

 to be remarked is, that, whilst the cavities of the body arc so configurated as exter- 

 nalhj to exhibit the most exact correspondency of the opposite sides, the contents of 

 these cavities have no such correspondency. A line drawn down the middle of the 

 breast, divides the thorax into two sides exactly similar; yet these two sides enclose 

 very different contents. The heart lies on the left side, a lobe of the lungs on the 

 I'ight, balancing each other neither in size nor shape. The same thing holds of the 

 abdomen. The liver lies on the right side, without any similar viscus opposed to it 

 on the left. The spleen indeed is situate over against the liver, but agreeing with 

 the liver neither in bulk nor form. There is no equi-pollcncy between these. The 

 stomach is a vessel both irregular in its shape and oblique in its position. The fold- 

 ings and doublings of the intestines do not present a parity of sides. Yet that sym- 

 metry which depends upon the co-relation of the sides, is externally preserved through- 

 out the whole trunk ; and is the more remarkable in the lower part of it, as the in- 

 teguments are soft ; and the shape, consequently, is not, as the thorax is by its ribs, 

 reduced by natural stays. It is evident, therefore, that the external proportion does 

 not arise from any equality in the shape or pressure of the internal contents. What 

 is it indeed but a correction of inequalities? — an adjustment, by mutual compensation, 

 of anomalou-s 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 inequahty in the feeding vessels is so managed, as to 

 produce no mequality of parts which were intended to correspond. The right arm 

 answers accurately to the left, both in size and shape ; but the arterial branches, 

 which supply the two ai'ms, do not go off from their trunk, in a pair, in the same man- 

 ner, at ihe same place, or at the same angle, under which waut of similitude it is 

 very dilficultto conceive how the same quantity of blood should be pushed through 

 each artery : yet the result is right ; — in the two limbs which are nourished by 

 them, we perceive no difference of supply, no effects of excess or deficiency. Con- 

 cerning the difference of manner, in which the subclavian and carotid arteries, upon 

 the different sides of the body, separate themselves from the aorta, Cheselden seems 

 to have thought, that the advantage which the left gains by going off at an angle 

 much more acute than the right, is made up to the right, by their going off together 

 in one branch. It is very possible that this may be the compensating contrivance : 

 and if it be so, how curious — how hydrostatical!" 



Many animals form singular and remarkable exceptions to this general law of sjTn- 

 metry. The MoUusca 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 their eyes are placed on that which is turn- 

 ed upperrvost, and this again is almost always the right side. Even in those animals 

 which arc 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 right side. Wc can observe this circumstance among the Crustacea ; we see it 

 in the side-walk of the Crab ; and remarkably so in the Pagurus Bernhardus, or Hor- 

 nut Crab, where the right forceps is larger than the left. We even see it in the 

 larger birds, and the feathers of the right wing are always stronger and of a better 

 quality than those of the left. The same inequality can be traced among the Mam- 

 malia, and in none of them more so than in Man, who is, perhaps, less ambi-dextrous 

 than any other animal, ^^'ith him the superiority of the right hand over the left is 

 not altogether the effect of habit, but is founded in nature. In walking, it is the right 

 leg and foot that give the greater impulse to the body ; in hopping or leaping, every 

 schoolboy, who is not naturally left-banded, uses his right leg in preference to the left. 

 Diseases of the right are more acute than those of the left side. "WTien a person 

 wishes to examine an object most minutely, he looks at it with one eye, and that is 

 almost always the right eye. ^^'hethe^ it be not a consequence of that more general 

 law, that a concentration of vital force in one organ is followed by a diminution of 

 vigour in others adjacent to it, and that the presence of the heart at the left side de- 

 prives that entire division of the body of the vigour enjoyed by the right side, we shall 

 not at present venture to determine. 



We have now shown that one general plan can be traced throughout the whole of 

 Living Beings ; that analogies, sufficiently precise, may be observed throughout the 

 Animal and Vegetable Kingdoms ; and that in every portion of created existence, we 

 find a degree of unity and perfection, a mutual dependence among their parts, and the 

 most exquisite symmetry in their forms. We shall now proceed to trace the analogy 

 perceptible in the essential functions of all these beings. Whether we examine 

 the arrangements for the continuation of the several species, the manner in which 

 that constant ingress and egress of particles, constituting nutrition, is fulfilled, the 

 temperature belonging to each class of beings, or that necessity which compels 

 every one of them to come in immediate contact with pure air, the results are the 

 sar.ie for all. It is only the details in the workmanship of the great artificer that vary, 

 but the same divine hand is perceptible throughout the whole. Thus, all Living Beings 

 require nutriment, but animals alone receive the food into central cavities, and digest 

 it. To all Living Beings air is equally essential — all absorb it and respire; but theia- 



strumcnts of respiration are 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 MoUusca, respire through gills or branchia;. 

 Insects, again, perform this function through trachea?, or minute holes, with which 

 their surfaces are perforated ; while many Worms and Polypi appear only to absorb 

 air through the pores of their skin, with which they are every where covered. Plant* 

 breathe through their leaves ; and many of them, deprived even of leaves, only perform 

 this function through the pores of the epidermis which covers their substance. 



Again, in respect to the arrangements for continuing the several species, we observe 

 the same general design, while the means arc ever various. How different do we see 

 this function in the Mammalia — those viviparous animals, where the youn"-, already 

 active and nearly perfect, immediately commence, from the moment of their separa- 

 tion from the parent, those instincts and actions, which can be terminated only by 

 death ; in the numerous class of oviparous, and in the ovo-viviparous animals ! Again, 

 how immense the chasm between all these animals just alluded to, and the lower beings 

 which are destitute of any distinctions of sex ! — how different is the function performed 

 by the Polj-pi, without sexes, without germs, producing their kind only by buds or 

 off-sets ! — 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 certain minute and almost 

 evanescent sporulcs or reproductive corpuscles. 



In all functions we trace this analogy in the end, and diversity in the means ; and 

 nowhere in a greater degree than in the functions peculiar to animals. They all 

 appear to feel, yet many possess no other organ of sensation than the skin. In very 

 many we find no brain, and in others not even can a vestige of nerves be traced. It 

 is evident that they all move spontaneously, yet in many we can find no visible marks 

 of muscles or organs of motion. We 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 Vertebratcd 

 Animals. 



The analogy among the functions and organs of these animals is so remarkable, and 

 the attention which has in consequence been paid to them so great, that we arc 

 exceedingly apt to form limited and erroneous views of the other parts of the animal 

 world ; — we expect to find in the lower animals the same parts, the same functions, 

 which 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 we in favour of the 

 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. 

 Tourncfort 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 we are all naturally disposed, on observing a great analogy in the functions 

 of all animals, to suppose them to be identical in their structure. 



Wc have said that the analogy among the Vertebratcd Animals is very remarkable. 

 They are all possessed of a spinal column, composed of numerous vertebra. Within 

 this solid column is lodged the spinal marrow, and it carries at one extremity a woU- 

 defcnded bony case or head, which contains the brain. In all these beings we find a 

 heart, red blood, lungs, or gills ; in all, the organs of the five senses arc seen in greater 

 or less degrees of perfection : wc find nerves, muscles, a digestive canal, more or less 

 complicated, aliverjind pancreas, with evident arrangements for continuing ihe spe- 

 cies. With the exception perhaps of one species, they all have their mouths dis- 

 posed horizontally ; and when they have limbs, these are always four in number. 

 This similarity prevails throughout their structure and functions. It is true that 

 their surfaces vary remarkably according to their several destinations, while the 

 orr^ans of motion differ greatly as they may be designed for swimming, flying, or 

 walking. The organs of respiration vary according as they are intended to breathe in 

 water or in the air. But these differences in external arrangement do not prevent us 

 from tracing the most exact analogy among them all. If wc take all the organs, 

 one by one, and compare them separately in any two vertebratcd animals, we shall 

 find the most exact equivalents in the two beings ; the analogy will be found perfect 

 in all the essential circumstances ; it is only the details which are observed to differ. 

 The fish at first sight appears to have neither neck nor thorax: but on inspecting it 

 more attentively, we find it to be possessed of all the series of vertebra; ; and that the 

 different pieces of its thorax are concentrated near the cranium, with which they are 

 almost confounded. IVI. Gcoffroy has 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 vertebrata and the aerial vertebrata, in 

 the organs of voice, of which the former are completely deprived. 



The principles, which must form the bases of a natural system of classification, have 

 been already explained. A luiowledge of internal organization, with the laws of the 

 subordination and co-existence of functions, will alone lead us to this result. 



Every function presupposes another function. Thus, when we sec a being appa- 

 rently moving voluntarily when irritated by any stimulant, we 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. We also conclude that 

 circulation presupposes respiration; because, wherever we find a heart, we also meet 

 with lungs, just in the same manner as we invariably find nerves wherever wc can dis- 

 cover muscles. In fact, Life is but an aggregation of phenomena produced by organs 

 connected and governed by these laws of co-existence. 



But in form.ing a system of classification, the difficulty consists in detecting the 

 law of subordination existing among the various combinations of these inslrumenid 

 of Life. Reflection upon the final cause or design of the functions will 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 hig 

 laboratory, and the "out-of-door" Naturalist, who haunts the wilds of Nature, 



