Sidebilder
PDF
ePub

523

The System of Nature.

524

Class 6th. Worms. Organs of motion | examination of the intentions of the natuexceedingly variable in number and posi- ralist. tion, not jointed; respiration without lungs or gills; substance soft; often both sexes in one individual; young from eggs. Heart without regular circulation, perhaps no heart; blood white, cold.

If our observations should be extended to the utmost limits of the living (and organized world, the transition would be easy to the vegetable creation, which differs not more from certain genera of the Mollusca (worms), than any two of these classes vary from each other. We should then possess seven principal orders, in which the division of living nature necessarily arrange themselves.

From the many thousands of individual species, which are comprised in the classes above enumerated, it is obvious that every attempt to study them separately and unconnectedly, must be fruitless; and therefore many efforts have been made to combine them into groups or orders; so that by keeping together those which are fitted with similar parts or organs, inquiry will be rendered easy, and the results be more completely retained. Two methods have been adopted for this purpose, each of which has had its followers; and which even now struggle for preeminence in the public mind. When it is stated, that one of these is a natural order, by which all the animated beings fall into a classification according to their forms and peculiarities; and that the other is an artificial arrangement, by which they are so distributed as to be of greatest advantage to the student, every inquirer who shall, for the first time, have this description of the separate methods submitted to his choice, will scarcely hesitate in giving the preference to the former. And yet, perhaps, a further experience will convince him that he has decided hastily.

In the science of language, a dictionary formed on the principle of classification, by which words should be arranged according to their roots, or their abstract meaning, would be a valuable production, highly useful to the accomplished scholar; but after all, only to be estimated and understood by him. Whereas, for practical purposes an alphabetical arrangement, where the words are jumbled together in confusion as to the meaning, with no principle of selection running through them but the arbitrary one, of modes of spelling, is found to be far the most useful even for learned grammarians. Such is also the fact in the science of nature; and the reason of it will be seen from even a slight

A distribution of the species into such groups as nature shall approve of, is the object he purposes to accomplish, when, after much study, he has been able to survey all the individual species of the kingdoms of nature; but before he can accomplish this, many years must pass, and some method must be adopted to secure his separate discoveries, previously to the full accomplishment of his object. At his outset he finds himself placed amidst an infinite number of unknown particulars; and in order to facilitate an acquaintance with them, he at once, without regarding individuals with much minuteness, throws together a number of them, which he calls a species, according to an assumed hypotheSIS. These he attempts again to combine by certain external eharacters, and calls them a genus. By these means he is enabled to contemplate and treat of them without being utterly bewildered in the labyrinth of unarranged individuals.

Classification is his filum Ariadneum,—— It was but imperfectly understood by the ancients; but it has enabled the moderns to arrive at conclusions with much more expedition than they, and with equal safety.We aim at two distinct objects by the use of system; we use the artificial for becoming acquainted with individuals, and the natural as the means of combining them.— Division and separation are the end of the artificial system; to establish agreement, is the end of the natural. The one is a descending, the other an ascending series. Now, wherever the object of the systematist is to enable his readers to discover species, it is unnecessary to define at every step; and where natural characters do not present themselves, we must adopt artificial ones. For this purpose large classes are formed, many of which necessarily are artificial. These again are broken up into orders, mostly of an artificial character; and thus the naturalist is led, step by step, from more comprehensive definitions to lessfrom class to order-from order to genusand from genus to species. In this descending series it will be observed, that the essential feature is the facility that is af forded for definition.

Hence the Linnean system of botany has succeeded so well, because its author selected, chiefly, as the ground of his arrangement, the number and proportion of parts most obvious, and least liable to vary. His classes and orders are avowedly so many assumptions, which practice has shewn to be convenient; but when we come to ge

[blocks in formation]

nera, the artificial system falls in with the natural, as Linneus framed their characters upon resemblances founded in nature."The mammiferous animals are arranged with more ease according to a natural system, in consequence of their number being comparatively small, and their forms strongly marked. Nevertheless, the system of M. Cuvier, in the Regne Animale,' clearly shews the vain attempt of finding a place for every thing. Nothing can be more satisfactory and beautiful than many of his orders and divisions; yet see how he is compelled to change his ground when he comes to the Pachydermata, and to huddle together species very remotely connected.— His birds also exemplify the same fact, where his order Passeres is made to include all that his other orders will not hold.”—( Bichen's Trans. of Lin. Soc. vol. 15.)

In forming the classes, already described, into subordinate divisions, such organs and parts as are essential to the nature of the creature, are chiefly regarded as the basis of a natural arrangement; for Almighty God having bestowed on his creatures dispositions and instincts, may well be supposed so to have framed and modified their organs, as shall best enable them to indulge those dispositions, and to carry their instinctive properties into action; and hence we may confidently presume, that those creatures which possess a similarity of form, will also be associated together in habits.— The formation and situation then of the snout and mouth, including the teeth, of the feet and claws, or hoofs, the form and nature of the tail, together with the form and situation of the teats, offer ready marks by which we may judge of the natural properties of an animal, and of the order and genus in which a naturalist will place it.— Nor need we in general go deeper than the surface, by having recourse to dissection, in order to acquire this information. Whereever animals agree or differ, a corresponding difference or agreement pervades their inmost structure; but this structure is to be known by some external marks; and, therefore, we are fortunately saved from the evil of being obliged to destroy a specimen, in order to discover its proper place in a system. The only certain exception to this (if indeed the exception be certain) is found in the natural group Tunicata, of the invertebrate order; of which some curious particulars may be found in a paper by Mr. W. S. Macleay, in the Trans. of Lin. Soc. vol. 14. The Gillaroo Trout, also, is most certainly distinguished from the varieties of Salmo Fario by its anatomy (See Salmonia,

526

by Sir H. Davy); but its external form has not been examined with sufficient minuteness to convince us that there is no external mark of distinction. At least, it differs much in form from the common trout of the rivers it inhabits, and, therefore, we may presume, from every other trout in existence.

Returning to the consideration of the classes of animals already enumerated, we find them naturally divided into certain groups or orders, that are as completely distinguished from each other as are the classes themselves. To afford an idea of these, among the orders in the Linnean class Mammalia, or such as suckle their young, the following well-known creatures may be selected as types of the respective races the ape, the lion, the dog, the hog, the mouse, the horse, the whale. Among birds, the parrot, the eagle, the raven, the sparrow, the partridge, the woodcock, the goose. Among the amphibia, the lizard, tortoise, dragon, frog, syren-snake. Among fishes, the shark, the chimæra, lamprey, pipe-fish, trunk-fish, cod-fish. In each of these classes or orders, the genera may be observed to refer analogically to each other; and it is further singular, that in each there is one corresponding group which exists in considerable excess above the others: these are the gnawers, (the mouse-tribe,) the finches (or warblers,) and the bony fishes, as the cod-fish and herring.

unable to Still, how

Proceeding further in our inquisition after separate groups of animals, we find that even those last enumerated, again multiply into subordinate divisions, equally distinguished from others of the same order, by their figure and habits; of which, as we do not purpose to institute an inquiry into the whole of the animal creation, the order first enumerated will serve as an example. It will be the more interesting to us, since man himself is included in it :-for considered only in reference to his body, we are separate him from the brutes. ever, man must be allowed to distinct genus, for there is enough to authorize this, even in his external organization; and as we are conscious of our own faculties, our consciousness fixes an eternal barrier of separation between ourselves and other genera of animals. was, no doubt, appointed by our Maker, that there should be the least assimilation of habits and regards, between man and those animals most like to him; whereas between him and some creatures that are of a dissimilar order, as the dog, a con

stand as a

It

[blocks in formation]

siderable intimacy exists. This is a merciful dispensation; for if the oran-outang had been admitted to the same fellowship as the dog, we know not what confusion might have been the result.

Man is distinguished from all the creatures of the genus Simia (ape,) and consequently from all others, by possessing two hands with separate thumbs, and two feet with flat nails on the toes.

Apes have four hands--what are termed feet, having in fact a separate thumb; they have no tail.

Baboons have four hands and a short tail; the body, assuming the figure of ordi. nary brutes of other orders, becoming narrow at the hips.

Monkeys have four hands and a long tail. Sapajous have the tail prehensile, but in some the thumb of the inferior hand is wanting.

In associating together the groups of this or any other order of animals, naturalists have found it convenient to fix upon a certain individual species, in which the organs by which the genus is characterized, are best developed, and to lay it down as the type. When this has been done by a skilful inquirer, it has been found that one of the species which naturally may be classed in the same group, departs from the type in certain of these points, and others in others, until each of the distinctive characters becomes so altered as to make an approach to some other perhaps distant genus; thus uniting together in harmony, groups of creatures, which, if the types only were considered, would seem utterly disjoined. In birds, where these characters have been most studied, the assimilation is made through the form of the bill, the feet, wings, tail; and also in the form of the body, and anatomical structure. The dissimilarity, or departure, is in each of these separately: thus, if among the species we begin with the hawk, which has a short, strong, and hooked-bill, a cere, short legs, feathered, strong claws, and long wings, we soon get to the eagle, in which the beak is elongated; to the vulture, in which it is still longer; and finally to the cormorant, a distinct race, in which the bill is longer and more slender, and the hook formed of a separate nail thus we may regard the falcon tribe, united to parrots by the beak and cere, to the pies, through the cuckow, by the bill and legs, to sparrows and thrushes by the butcher-birds, to the waders by the secretary vulture, to the swimmers by the sea-eagle and cormorant or gannet, to gallinaceous birds by the turkey

528

buzzard, to the owls, both in form and sluggishness, by the buzzard; and, as the owl itself is the type of another genus, though it is connected with the goatsucker and the swallow, a little innocent creature, which at first view could scarcely be supposed connected in form or habit with such ferocious depredators.

We have here also a glance at what seems to have proved a stumbling-block to some inquirers; the existence of parts or organs, that certainly are not of the least practical utility to the creatures that possess them. That such organs are to be found, will perhaps be judged incredible, and the supposition be pronounced an imputation on the wisdom of Him who has made nothing in vain, by some minds. The assertion is, however, confined to this, that they are not of practical utility to the creatures that possess them; and the breasts in man may be given, as one instance among many, in proof of the fact. It by no means follows, however, that they are not essentially necessary to the general harmony of nature; since by means of such supernumerary organs in many animals, we are able to trace a connexion of affinity, in what may be denominated its vanishing point, with others, in which the organs are more developed, and of necessary use. Among insects also, the connexion of affinity is sometimes found in one stage of their existence, and not in another; in the pupa, and not in the winged animal; and among amphibia, the frog is related to the fish when young, but the connexion is lost when it is old.

But whilst we feel gratified at the discovery of such harmonious affinities, by which the separate groups, or genera of a class, are assimilated into a whole, our wonder is not so great as when we perceive the same principle of connexion operating with undiminished energy under the most unpromising circumstances. To connect together the different genera of a class, seems no difficult task, since each of the classes has its peculiar organs; and a modification of them to a vast extent, is easily imagined. When, however, the Eternal Infinite is to act, easy and difficult are terms of no meaning; and discordant forms easily approach each other under his plastic hand. To follow up the law of affinity already laid down, whereby whilst certain genera (and also some of each genus) are only connected to others of the same class, others shall carry the similarity beyond its bounds; we may instance, as striking illustrations of this principle, things which, but for this cause,

529

The System of Nature.

530

must have been considered only as freaks | but of which one species was no larger than the hare :-the anoplotherium, which in nature approached ruminant animals, but of which, one species had a tail like that of the kangaroo:-all these, and more, (some probably not yet discovered,) give us to see, that at the first, the systematic arrangement was complete; and now, so long after they have ceased to inhabit our earth, their forms are drawn from the museum of the great Architect, to astonish us, on whom the ends of the world are come, with the display of that beautiful symmetry, which in the beginning pervaded the whole.

of imagination. Such are, that the classes of quadrupeds and birds are connected, so far as regards the wings, by means of the bat; as regards the bill, by the ornithorhynchus, the legs and feet, by means of the jerboa. In the tail of some squirrels, the hair assumes the appearance of a feather, and in the porcupine we have the quill. So far we see the affinities carried off from the beasts; among birds they are met by the legs of the giraffe in the steltplover, the legs and feet of the camel in the ostrich, claws of the cat in the hawk, hair of a quadruped in the cassowary, softened and elongated snout in the spoonbill, and the absence of wings in the penguin. What the bat is to quadrupeds, uniting their habits to those of birds, the whales are to fishes; on the other hand, the ostrich is a corresponding link on the part of the feathered creation, and the angler on the part of fishes. The foot-like ventral fins, in all the species of the genus Sophius, and claws on the pectorals in one, are a near approach to the form of a beast.

But whilst we have been extending our inquiry into the connexions which exist among the classes, orders, and genera of natural beings, it cannot fail to strike the observer, that some creatures are found to stand out, as it were in high relief, from those with which they are surrounded; so that they seem to have little affinity, not only with other classes, but even with those species with which we should be disposed to associate them. This may be said of the elephant, rhinoceros, and a few other of the larger quadrupeds. Could we suppose these creatures to afford exceptions to a general law of nature, we should wonder at the anomaly, and regard it as a defect in the harmony of creation. But we are indebted to the discoveries of late years, for the removal of the difficulty. This has partly been effected by the discovery of several creatures in New Holland and the East, whereby gaps have the discoveries of organic remains of a been filled up: but more especially by considerable number of those very creatures that are wanting in the living system. The circumstances under which so many animals have become extinct, are foreign to this inquiry; but some probable surmises on the subject are contained in a paper in the Imperial Magazine, vol. iv. col. 35. The great animal of the Ohio, the Siberian mammoth, the palæotherium, which in its form unites the tapir, and consequently the elephant, with the horse,

138.-VOL. XII.

Nor are the affinities of these hitherto solitary quadrupeds all that have been developed. Creatures which now stand at the greatest distance, were once connected by living affinities. Reptile quadrupeds, (amphibia,) have been found, belonging to the same group with the great natural order of lizards; but differing most essentially in structure from all the now existing genera, and in such a way as must have fitted them to live exclusively in the sea. They appear, therefore, to bear the same relation to living lizards, that the whale tribe bear to other mammalia. A genus of lizards has been described, which is marked by the excessive elongation of the fourth toe, in front. It is hardly possible to doubt, says Mons. Cuvier, (who has given the name of pterodactyle to the creature,) that the long toe served to support a membrane, which furnished the animal, over the whole length of the foreleg, with a much more powerful wing than that of the dragon, (Draco volansdin,) and at least equal in strength to that of the bat. This ancient animal could fly with a vigour proportional to its muscular power; and then it could make use of its short toes, armed with crooked claws, to suspend itself from trees. In the standing posture, it could make little use of its forelegs, and perhaps always kept them folded up, as birds do their wings; it could, however, also employ its small fore-toes for hanging itself to branches of trees, though its posture of repose must have been usually on its hind-feet, like that of birds. It must, moreover, have held its neck reverted, to prevent its enormous head from upsetting its equilibrium. Still further to point out this genus, as the connecting link between lizards and birds, one species has been discovered with a short beak. In the Icthyosaurus, we have the muzzle of a dolphin, teeth of a crocodile, head and breast of a lizard, paws of a cetaceous animal, or paddles of

2 L

531

Sir Humphry Davy's Lectures.

a turtle, and vertebræ of a fish. In another species of the same genus, with the same turtle paddles, we have a lizard's head, and a long neck like the body of a serpent. These creatures breathe air, not water; but they could not travel on land. The plesiosaurus has a small head, but the longest neck of any creature, giving it the likeness of a serpent. The body seems to have been like that of the lizard, but with fins like the whale tribe, and, like them, with nostrils on the top of the head.

As the Imperial Magazine is a compendium of scientific information, very extended and intricate disquisition will not be sought in its pages; but so much as has now been laid before its readers, will enable them to see how great a fund of information lies ready to the hand of those who will labour in this mine of knowledge. And, whilst we admit, that the volume of the revelation of God's will, has the first claim on our attention, that other revelation, which so well displays his eternal power and godhead, is surely worthy of more examination, than it receives from those who pursue the inquiry merely as an amusement. We see also, that a branch of science, on which infidelity has dared to lay its hands, as peculiarly its own, (geology,) may be made to bring its contributions also, to the corroboration of the same fact, that the Creator is One, and that the harmony we see between the living and the dead, is a proof that they have all sprung from one hand, acting on an harmonious plan; and not, as some would have it, in fits and starts of creation and destruction, without motive, and without end. Polperro.

J. C.

NOTES OF THE FOURTH LECTURE OF SIR HUMPHRY DAVY, ON HIS ELECTROCHEMICAL DISCOVERIES, DELIVERED IN DUBLIN, NOVEMBER 10, 1810.

Compendium of the last Lecture.

(Continued from col. 490.) ELECTRICITY is exerted in various matters, particularly in metals, by contact. All these discover two properties, viz. positive, and negative; which properties, already explained, were first called the Vitreous and Resinous electricities, and are only the properties of ATTRACTION and REPULSION in these circumstances, of similar or opposite states of electricity.

It requires a dry and almost empty room to observe these phenomena, when caused merely by single plates of metal,

532

or other substances. Glass is positive to silk, and silk positive to sealing-wax. A solution of liver of sulphur in a silver cup, gives a violent contraction to the crural nerve of a frog's leg; on contact with the exterior of the cup, the sulphur gives the silver a negative charge. It is so strong a shock, as to affect the fingers of the person who holds the frog.

There is scarcely a body in nature, which does not contain electricity. Even air being discharged or propelled on the plate of an electrometer, is found to give a slight shock.

Probably oxygen is negative, and nitrogen positive. The tourmalin stone is an hexagonal prism with pyramidal base; if held by the middle before a fire, it be comes electric. Water rising in vapour gives negative electricity to the electrometer, but descending in condensation it gives positive. All crystallized gems are small electric machines.

What are the principles of electricity? Some philosophers supposed a fluid, which has not been demonstrated, and never can be more than an hypothesis. Some say it is mechanical, and that the motion of the wheel from the silk draws it out by friction. This coarse idea does not account for the extent and phenomena of electricity. Others say that chemical changes produce electric changes. This is not defensible: there is no chemic change in the glass and wax. Professor Davy seems to think, that electric changes produce chemic changes; that chemistry is secondary to electrical action, and is to be referred to the same causes with gravitationto some simple, unknown principle, as the watch, though moving by the action of a spring on the wheels which direct the index, must still be dependent on the ARTIST who formed it; and as music, however explained by the laws of harmony, depends on the skill of the musician.

When a conductor is connected with the earth, it is in a negative state: the pith balls repel each other at the approach of sealing-wax, and a hand makes the spark, because connected with the earth-but an insulated machine is the reverse.

In every conductor, one end of it is negative, the other end is positive, and the middle neutral: this is shown by a pair of pith balls, mounted on pivots of wire at the ends and middle; and if there was a series of conductors connected to any member, the fact in each or the whole is similar. Hence its similarity to Voltaic electricity; and even the Leyden jar is positive on its interior, and nega

« ForrigeFortsett »