When the Almighty Creator willed to bring into existence this mundane system, he formed it according to a preconcerted plan, with all its parts beautifully linked together and mutually corresponding. All things were ordered in measure, and number, and weight[1129]. There was nothing deficient, nothing superfluous; but the whole in the strictest sense "was very good[1130]," and calculated in the highest degree to answer the purpose of its Great Author. I call it a system of Correlation, because there is discernible in it, in the first place, a concatenation of its parts, by which, as to their forms and uses, objects are linked together in groups by a chain of affinities; so that we pass from one to the other by gentle gradations, without having to overleap any wide interval. We see also a gradual ascent from low to high, from less to more excellent. And this leads us to another kind of relationship between natural objects, by which, though placed in distinct groups or in a different series, they in some sort represent and symbolize each other. Examples of this relationship by analogy are to be found in every kingdom of nature, and often form an ascending series from the lowest to the highest; for, as we shall see hereafter, these resemblances appear to maintain a certain correspondence with each other as to their relative situations; so that, for instance, in the animal kingdom they ascend step by step, without being linked by affinity or having any real juxtaposition, from the lowest groups, towards man, who stands alone at the head, or in the centre of all.—I shall say something on each of these kinds of relationship.
I. The relation of affinity may be considered as to its series and groups. A series, of course, consists of parts either concatenated like a chain, or placed separately at small intervals from each other. It may run either in a right line, or deviate from it in various ways. It appears to be the opinion of most modern Physiologists, that the series of affinities in nature is a concatenated or continuous series; and that though an hiatus is here and there observable, this has been caused either by the annihilation of some original group or species in consequence of some great convulsion of nature, or that the objects required to fill it up are still in existence but have not yet been discovered[1131]: and this opinion is founded on a dictum of Linné, Natura ... saltus non facit[1132]. If this dictum be liberally interpreted, according to the evident meaning of the word saltus, few will be disposed to object to it; since both observation and analogy combine to prove that there must be a regular approximation of things to each other in the works of God; and that could we see the whole according to his original plan, we should find no violent interval to break up that approximation: but if it be contended, that in this plan there is no difference in the juxtaposition of the nearest groups or individuals, and never any interval between them, I think we are going further than either observation or analogy will warrant. Were this really and strictly the case, it seems to follow that every group or individual species must on one side borrow half its characters from the preceding group or species, and on the other impart half to the succeeding[1133]. But one of the most evident laws of creation is variety; and if we survey all the works of the Most High, we shall no where discover that kind of order and symmetry that this strict interpretation implies. The general march of nature therefore seems to say, that there must be varying though not violent intervals in the series of beings: or in other words, some conterminous species or groups have more characters in common than others.
It was the opinion of Bonnet (in this field himself a host) and many other Naturalists, that the series of beings was not only continuous, but undeviating, ascending in a direct line from the lowest to the highest[1134]. Others, finding that this theory could not be made to accord with the actual state of things in nature, thought that a scale of the kingdoms of nature must represent a map or net[1135]; thus abandoning a continuous series: and Lamarck, as was before observed[1136], for the solution of the difficulty, arranged Invertebrate animals in a double subramose one. Mr. W. S. MacLeay and (without consultation nearly at the same time) Professor Agardh, Mr. Fries, &c. have given to the learned world an opinion which approximates more nearly to what we see in nature: viz. That the arrangement of objects is indeed in a continuous series, but which in its progress forms various convolutions, each of which may be represented by a circle, or a series that returns into itself[1137]. According to this opinion,—which seems the most consistent of any yet advanced, and which reconciles facts which upon no other plan can be reconciled,—the series of beings is involved in the highest degree, rolling wheel within wheel ad infinitum, and revolving, if I may so speak, round its centre and summit—man[1138]: who, though not including in himself all that distinguishes them, is still the great Archetype in which they terminate, and from which they degrade on all sides.
It is by this convolving series that the various groups into which the kingdoms of nature seem resolvable are formed. We are instructed by the highest authority that every thing was created "after its kind;" and the common sense of mankind in all ages has imposed classic, generic, and other names implying sections, as well as specific ones, upon natural objects: and though many modern Physiologists have asserted that species form the only absolute division in nature; yet as all seem to allow that there are groups, and many that these are represented by a circle or group returning into itself[1139], the most absolute division in nature, we will not contend for a term[1140]. We now come to consider these groups themselves, and may notice them under various denominations.
It is customary to consider all the substances of which our globe consists as divided into three kingdoms,—the Mineral, Vegetable, and Animal; but strictly speaking the primary division is into organized and inorganized matter; the former resolving itself into the two kingdoms last mentioned. These, like England and Scotland of old, have their "Land Debateable;" occupied by those Productions moyennes, (to use a term of Bonnet's[1141],) which are as it were partly animal and partly vegetable. From this territory common to both, the two kingdoms are extended in a nearly parallel direction till they reach their extreme limits, without any incursion from either side upon their mutual boundaries, but each showing its kindred with the other by certain resemblances observable between opposite points; so that valley corresponds with valley, mountain with mountain, river with river, sea with sea[1142]; not, however, so as to form an exact counterpart, but only in some general features. But to leave metaphor;—as the vegetable kingdom is distinguished from the mineral by its organization and life, by its circulation of sap, and by its powers of reproduction by seed or otherwise; so is the animal from the vegetable by its powers of volition and locomotion[1143], by its nervous systems and organs of sensation, and the senses to which they minister, by its muscular irritability, and by its instinctive endowments.
Having made these observations with regard to the primary division of natural objects in general,—what I have further to say will be confined to the animal kingdom, and ultimately to the branch of which we are treating.
i. Lamarck divided the animal kingdom into two provinces, or subkingdoms as they are now called; the one consisting of all those animals whose skeleton is internal and built upon a vertebral column, which are denominated Vertebrates; and the second, of those whose skeleton or its representative is for the most part external, including the muscles,—these are called Invertebrates[1144]. Though this distinction is so marked as in general to form a most striking characteristic, yet when these two provinces approach each other, it begins to disappear. Thus the vertebral column, forming one piece with the shell[1145], becomes almost external in the Chelonian reptiles, or tortoises and turtles, and almost disappears in the cyclostomous fishes; and there is the beginning of an internal one in the Cephalopoda, or cuttle-fish belonging to the Invertebrates. Dr. Virey, assuming the nervous system as his basis, long since divided the animal kingdom, without assigning names to them, into three subkingdoms[1146]; M. Cuvier has four—Vertebrata; Mollusca; Articulata; Radiata[1147]: and Mr. MacLeay, finding five variations of that system, divides animals into five provinces or subkingdoms, of which I formerly gave you some account[1148];—viz. Vertebrata, in which the nervous system has only one principal centre; Annulosa, in which it is ganglionic, with the ganglions arranged in a series, with a double spinal chord; Mollusca, in which it is ganglionic, with the ganglions dispersed irregularly but connected by nervous threads; Radiata, in which it is filamentous, with the nervous threads radiating from the mouth; and Acrita, in which this system is molecular[1149]. And to this division of the kingdom, as founded on a satisfactory basis, I should recommend you to adhere: still however we may speak of vertebrate and invertebrate animals, as forming the primary subdivision of them, taken from a striking character and obvious to every one who sees them.
If you inquire into the rank of each of these subkingdoms, of course you will assign the principal station to the Vertebrates, which are the most perfectly organized, to which man belongs, and over which he immediately presides. If we form the scale according to the nervous system of each province, that in which the organ of sensation and intellect is most concentrated will stand first; and in proportion as this organ is multiplied and dispersed will be the station of the rest, which will place them in the order in which I have mentioned them; and the Annulosa, to which insects belong, will precede the Mollusca, which Cuvier and Lamarck had placed before them on account of their system of circulation. But when we reflect that a heart and circulation occur in some of the conglomerate Polypi[1150], animals that approach the vegetable kingdom; that some of the acephalous Mollusca have no visible organs of sense, except that of taste, whose substance is little better than a homogeneous gelatinous pulp, and who seem from their inert nature to have very slight powers of voluntary motion[1151], we shall be convinced that a heart and circulation alone, unaccompanied by a more concentrated nervous system and more perfect structure, cannot place an animal above those which in every other respect so obviously excel them. With regard to insects particularly, we may further ask—Who that considers how man employs his powers and organs even in his most degraded state, or that contemplates the wonderful works that he is enabled to accomplish when his faculties receive their due cultivation and direction, can avoid regarding him as superior to the rest of the animal creation? And what unsophisticated mind, not entangled in the trammels of system, when it surveys the industry, the various proceedings, and almost miraculous works that have been laid before you, the waxen palaces of the bee,—the paper cottages of the wasp and hornet,—the crowded metropolis of the white ants,—the arts, the manufactures, and stratagems of other insects,—the associations and labours for the common good of those that are gregarious;—will not at once conclude that they must be a superior race to the slug, the snail, and others, which live only to eat and propagate their kind?
Or who, that considers the wonderful structure of the animals whose cause I advocate,—the analogy that exists between their organs of manducation, of motion, and of sensation, and between various other parts of it[1152], with those of the higher animals,—the acuteness of their senses, their wonderful strength of muscle[1153], and powers of locomotion[1154],—but will think them superior to the headless and almost inanimate oyster or muscle, or the conglomerate Alcyonia, though they have a heart and circulation?
Who again, that observes that in proportion as pedate animals approach to the human type, their motions are accomplished by fewer organs,—that man walks ore sublimi upon two legs; the majority of quadrupeds upon four; insects upon six: the Arachnida apparently upon eight; most Crustacea upon ten; and the Myriapods and others upon many,—but will thence conclude that insects must precede the Arachnida and Crustacea?