Part 26

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_?

Who, once more, that reflects that if any of the superior animals are deprived of a limb it can never be reproduced, and that in insects the same circumstance occurs; while spiders and _Crustacea_ if they lose a leg have the power of reproducing it, and the _Mollusca_ if they are decapitated can gain a new head,--will consent to their being placed after any of these animals[1155]?

Lastly, who that recollects that the _Mollusca_ are hermaphrodites, like most plants, bearing both male and female organs in the same body,--but will allow that insects, in which the sexes are separate as in the Vertebrates, must be more perfect, and of a higher grade[1156]?

ii. We now come to the _Classes_ into which the _Annulosa_ are divided. This term appears first to have been employed by Tournefort, and was adopted by Linné[1157]. As the nervous system of animals furnishes the most prominent distinction of a subkingdom, so the _circulation_ of their fluids, and their _respiration_ necessarily connected with it, seems best to point out the _classes_ into which it may next be resolved. But having fully explained my ideas on this subject in a former letter, I need not here repeat what I then said[1158].

iii. As we have subkingdoms, so we may also have _subclasses_, or such large divisions of a class--not founded upon internal organization or any of the primary vital functions, but upon different modes of taking their food, or such other _secondary_ characters--as include more than one _Order_. To this description Clairville's _Mandibulata_ and _Haustellata_ appear to me to belong, which I think are by no means entitled to the rank of Classes; for whoever compares these two tribes together will at the first glance be convinced, by the numerous characters they possess in common, notwithstanding the different mode in which they take their food, that they form one connected primary group. This circumstance, therefore, only furnishes a clue for their further subdivision into two secondary groups, separated by distinctions certainly of a lower value than those which separate the _Crustacea_ and _Arachnida_ from _Insecta_. This is further confirmed by the variations that take place in their mode of feeding in their different states; some from masticators becoming suctorious (_Lepidoptera_), and others from being suctorious becoming masticators (_Myrmeleon_, _Dytiscus_, &c.),--which shows that this character does not enter the essential idea of the animal.

iv. Next to Classes and Subclasses we are to consider those groups of insects that are denominated _Orders_. The characters of these at first were taken principally from the instruments of flight or the absence of them; and the name appropriated to each Order by Linné, after Aristotle, had reference to this circumstance. But this alone does not afford characters sufficiently discriminating: for though to an accurate observer a difference in these organs appears to be characteristic of most of the Orders, yet in some it is not easily detected or defined. In the _Neuroptera_ there are as many different types of wings as there are of tribes or suborders. So that it seems not possible so to construct the definition of every Order, as to take its character from the organs of flight alone. Linné was sensible of this, and was compelled to have recourse to subsidiary characters in the majority of his: his observation therefore with regard to _Genera_,--that the character does not give the genus, but the genus the character[1159],--applies equally to _Orders_; and the characters included in the definition of an Order, should be the result of a careful examination of its component groups.

On a former occasion I named to you the Orders into which it appeared to me the Class _Insecta_ might be divided[1160]; they were these. _Coleoptera_; _Strepsiptera_; _Dermaptera_; _Orthoptera_; _Hemiptera_; _Trichoptera_; _Lepidoptera_; _Neuroptera_; _Hymenoptera_; _Diptera_: _Aphaniptera_; _Aptera_. I then briefly explained them merely for the sake of illustration, and that you might know what description of insects were meant when these Orders were mentioned in my letters, without intending to affirm that I had arranged them in a natural series, or that all of them were perfectly natural. I shall now consider them separately, and conclude with giving my sentiments as to which should be placed first.

* _ORDERS in which the ordinary Trophi all occur, or the_ Mouth _is_ perfect[1161]. (_Mandibulata._)

1. COLEOPTERA[1162] (_Eleutherata_ F.). Aristotle may be called the founder of this Order, since he both named and defined it[1163]. Both his name and definition were adopted by Linné; and the former (with the exception of Fabricius and his school) by all succeeding Entomologists. To his definition _Wings in a sheath_[1164], other characters have been added; as the folding of the wings, and the straight suture by which the elytra are united[1165]. Aristotle's character, though to be found in the great majority of the Order, is not universal, since there are some beetles that have neither wings nor sheath, as the female glow-worm; and many that though they have the sheath have no wings, as _Meloe_, many _Carabi_, &c. To the transverse folding of the wings there are also exceptions; as in _Buprestis_, _Molorchus_, &c. The straight suture by which one elytrum exactly coincides with the other without lapping over, fails in _Meloe_: so that no one of these characters can be called universal in the Order; but as an exception or two does not invalidate a rule, and these are sufficiently universal for the purpose of pointing it out, they may be retained. Perhaps it will be an improvement to add the kind of the _metamorphosis_, which, as far as known, prevails universally.

DEF. _Metamorphosis_ incomplete[1166].

_Legs_ inosculating, posterior coxæ usually transverse.

_Elytra_ corneous, or coriaceous, without veins, united by a straight suture, so as mostly to cover the wings completely[1167].

_Wings_ longitudinally and transversely folded[1168]: _neuration_ simple[1169].

2. STREPSIPTERA[1170] (_Rhiphiptera_ Latr.) The characters of this Order were first given in the _Linnean Transactions_, and it has been adopted by Latreille, who however, without sufficient reason, has changed the name originally imposed to _Rhiphiptera_[1171]. Rossi, who was the first that discovered an insect of this Order, concluded that because it was parasitic it must be _Hymenopterous_; and it is certainly more nearly related to that Order than to the _Diptera_, amongst which M. Lamarck has arranged it, and with which it has no character in common, except having two wings. This is one of those Orders, consisting of few genera and species, which, from their connecting two circles, Mr. MacLeay has called _osculant_, who places it between the _Hymenoptera_ and _Coleoptera_[1172].

DEF. _Metamorphosis_ subincomplete[1173]?

_Pseudelytra_ twisted, attached to the anterior leg[1174].

_Wings_ not covered by the elytra, longitudinally folded, forming nearly the quadrant of a circle[1175]: _neuration_ simple.

_Anus_ styliferous[1176].

3. DERMAPTERA[1177] (_Ulonota_ F. _Orthoptera_ Oliv.). This is another osculant Order, evidently connecting the _Coleoptera_ with the _Orthoptera_. The elytra are of a coriaceous substance, have a straight suture, and are not veined, and the wings are folded longitudinally as well as transversely,--circumstances which connect it with the former Order,--while the shape of its wings, its oral organs, and its metamorphosis, show its affinity to the latter. It was established at the same time and in the same work with the preceding Order, in pursuance of a suggestion of Dr. Leach, and consists solely of the Linnean genus _Forficula_.

DEF. _Metamorphosis_ semicomplete.

_Elytra_ coriaceous, without veins, united by a straight suture, so as partly to cover the wings.

_Wings_ longitudinally and transversely folded, each forming nearly the quadrant of a circle: _neuration_ radiating[1178].

_Anus_ forcipate.

4. ORTHOPTERA[1179] (_Ulonota_ F.). This Order, which Linné at first regarded as belonging to the _Coleoptera_[1180], and afterwards improperly added to the suctorious _Hemiptera_, was very judiciously separated from both by De Geer, under the name of _Dermaptera_, a name not improper, and which ought to have been retained. Its present name was, I believe, assigned to it by Olivier; and as this is generally in use, I shall not attempt to disturb it. Dr. Leach divided the Order into two, separating the _Blattina_ from it, under the name of _Dictyoptera_[1181]. He was led to this by the tegmina decussating or lapping obliquely over each other, whereas in the rest the horizontal portion of one tegmen lies longitudinally over that of the other; he also probably took their depressed body into consideration;--these circumstances, however, rather indicate a _tribe_ or suborder; and as such Mr. MacLeay regards it.

DEF. _Metamorphosis_ semicomplete.

_Legs_ suspended.

_Tegmina_ generally pergameneous[1182], reticulated with nervures, more or less incumbent, covering the wings.

_Wings_ longitudinally folded, ample: _neuration_ reticulated.

5. NEUROPTERA[1183] (_Synistata_, _Odonota_ F.). Of all the Linnean Orders this appears to consist of the most discordant tribes; so that it seems next to impossible to construct a definition that will include them all, unless indeed we admit M. Latreille's idea, adopted by Mr. MacLeay[1184], that a varied metamorphosis is its essential character; or, to speak more largely, variety itself seems the characteristic of the insects composing it, in every state; and there is scarcely a common distinctive character in their perfect state, upon detecting which in any individual you may exclaim--This is a Neuropterous insect. The only one that I have been enabled to seize is, that their _scapulæ_ and _parapleuræ_ are parallel and placed obliquely[1185]. Whether, with all this puzzling variation and dissonance between the different tribes of which it is now composed, this Order can be considered as a natural group, in the present state of our knowledge it would be rash to decide. I shall observe, however, that the _Libellulina_,--whether we regard their metamorphosis and the singular character before described that distinguishes their larva and pupa[1186], their oral instruments[1187], the remarkable position of their legs[1188], their general form, the wonderful and peculiar machinery by which their wings are moved[1189], and other circumstances of their internal anatomy,--if any are to be regarded as forming a separate Order, are the first entitled to that distinction. At present, with our friend Mr. MacLeay, I shall consider it as not further divisible, and as consisting of five principal forms. I must not omit to observe, that in the _Ephemerina_ the parts of the mouth, except the labrum and palpi, appear to be mere rudiments[1190].

DEF. _Metamorphosis_ varying. _Larva_ a hexapod.

_Wings_ four in most, and reticulated with numerous areolets.

_Prothorax_ distinct.

_Scapulæ_ and _Parapleuræ_ parallel and oblique.

_Tail_ of the female without a terebrant, or pungent multivalve ovipositor[1191].