Part 27

6. HYMENOPTERA[1192] (_Piezata_ F.). Mr. MacLeay considers _Sirex_ L. as being osculant between the Order we are now entering upon and the _Trichoptera_, and _Tenthredo_, L. as belonging to the latter. He appears to ground this opinion chiefly upon a consideration of their larvæ and a slight difference in their ovipositor. As the Order, as settled by Linné, has always been deemed one of the most natural ones, and all the great Entomologists of the present æra have agreed with him in thinking it so; it seems to me that to prove them mistaken in this opinion, the question should have been discussed at more length, and that it requires arguments of more weight than any Mr. MacLeay has at present produced to set it aside. He appears in general to lay great stress upon an agreement in larvæ and the kind of metamorphosis; and I am ready to acknowledge that it forms a strong _presumption_ in favour of any hypothesis of affinity between certain tribes. But when it is had recourse to as fundamental and infallible, I think it is pushed far beyond what it will bear, or is warrantable. I may be wrong; but in my apprehension, a striking agreement in their general structure in the _perfect_ state, which is the acme of their nature, affords a much more satisfactory reason for keeping two tribes together, than any difference observable in their larvæ or metamorphosis, for separating them. Let any one compare the structure of these two tribes with the _Trichoptera_ on one side, and the _Hymenoptera_ on the other, and it will require but a glance to convince him of their greater affinity to the latter; and the simple inspection only of Jurine's plates of the wings of _Hymenoptera_ is calculated to produce the same effect. With regard to their _larvæ_, the resemblance between the case-worms and the pseudo-caterpillars of the saw-flies seems to me very distant, and the numerous prolegs of the latter have scarcely a legitimate representative in the former. The larvæ of the genus _Lyda_ lose the prolegs intirely, and in one species, which much resembles the vermiform larvæ of _Hymenoptera_, the real legs are so extremely short as to be scarcely discernible[1193]; so that it requires no great stretch of faith to believe that saw-flies or _Sirices_ may exist in whose larvæ the legs disappear[1194]. But it is this very tribe, whose larvæ thus approach to those of the other _Hymenoptera_, in which Mr. MacLeay finds the greatest external resemblance to the _Trichoptera_[1195]. In fact the difference between the saw-flies and _Siricidæ_, and the remainder of the _Hymenoptera_, amounts to little more than what takes place in the _Diptera_ Order between the _Tipulidæ_, _Asilidæ_, _Muscidæ_, &c., in which also the _metamorphosis_ differs.

Another argument upon which Mr. MacLeay seems to lay some stress, is taken from the number of parts into which the _ovipositor_ of the saw-flies is resolvable, which he finds to consist of _four_ pieces; while in what he considers as the genuine _Hymenoptera_, it is formed only of _three_[1196]: but in fact, in these last there are _two_ spiculæ, answering to the two saws of _Tenthredo_, so that the vagina in which these move may be considered as a _double_ sheath: only, as these were to be pushed out at the _same_ time, and the others _alternately_, it was necessary that in the latter each sheath should be separate, to admit of this motion; but as to its composition, the weapon in both is essentially the same. At any rate this structure could furnish a reason only for the formation of a separate group in the _same_ Order, but none for the transfer of such group to _another_, which had no such instrument at all; since, as we have seen, the _Trichoptera_ extrude their eggs at once in a mass[1197]. I do not mean, however, that it should be inferred from what I have here said, that there is no _tendency_ in the saw-flies towards a Trichopterous type, for in them nature seems pointing that way, but the distance is too great, and the number of types of form necessary to fill up the interval too many, to warrant in my opinion their removal from the one Order to the other.

DEF. _Metamorphosis_ incomplete[1198].

_Trophi_ in most not used for mastication[1199].

_Wings_ four: _neuration_ generally areolate[1200].

_Prothorax_ obsolete, giving place to an ample collar.

_Tarsi_ pentamerous.

_Ovipositor_ 5-6-valved, the vagina darting forth two retroserrulate spiculæ.

** _ORDERS in which all the ordinary Trophi do_ not _occur, or the_ Mouth _is_ imperfect[1201] (_Haustellata_).

7. HEMIPTERA[1202] (_Ryngota_ F.). Linné at first confined this Order to those insects which have a _promuscis_, which he denominated a _rostrum_[1203]; but afterwards, convinced that the _Orthoptera_ of the moderns could not be associated properly with the _Coleoptera_; instead of forming them into a distinct Order, as nature would have dictated--perhaps to avoid the multiplication of Orders and without altering his definition--with equal infelicity he added them to this. Subsequent Entomologists, who saw the impropriety of masticating insects thus herding with suctorious ones, restricted the Order to its old limits; but Latreille very judiciously altered its arrangement, and divided it into two Sections, separating those whose hemelytra terminate in membrane, from those in which they are mostly tegmina, or of a substance intermediate between that of the elytra of _Coleoptera_ and that of the wings of the Tetrapterous Orders. He denominated the first of these sections, or rather suborders, _Heteroptera_, and the last _Homoptera_[1204]. Dr. Leach, observing that very considerable differences take place both in the economy and structure of Heteropterous and Homopterous insects, followed De Geer in considering them as separate Orders, which he has called _Hemiptera_ and _Omoptera_, and in which he has been followed by Mr. MacLeay; who, however, with his usual accuracy and judgment, has restored the aspirate to the latter name[1205]. Their agreement in having a _promuscis_, or instrument of suction, with a jointed sheath, at present induces me to hesitate as to the propriety of their separation, and to consider them as forming _secondary_ rather than _primary_ sections of the Class. That you may be enabled to judge for yourself upon this subject, I will state the principal features in which they differ. In the first place, the Heteropterous section usually sucks the juices of _animals_, and the Homopterous, those of _plants_; in the former, the _Hemelytra_, besides their different substance, as well as the wings, cross each other; while in the latter, the organs of flight are deflexed, and do not lap over each other at all. The antennæ also of the one are often long, and do not terminate in a _bristle_; while in the other, with few exceptions, they are very short and setigerous. In the _Heteroptera_ the body is depressed and flat, in the _Homoptera_ convex and thick. In the former, the scutellum is one of the principal features of the trunk; in the latter, not at all remarkable[1206]. Other differences in the structure, both of head, trunk, and abdomen, might be pointed out; but these you will chiefly find noticed in my letters on the External Anatomy of Insects, where I treated of those parts. I shall here, therefore, only further mention the ovipositor also as forming a most striking distinction[1207].

DEF. _Metamorphosis_ semicomplete in almost all.

_Mouth_ promuscidate[1208].

_Wings_ covered by _Hemelytra_ or _Tegmina_[1209].

_Tarsi_ mostly trimerous, rarely dimerous or monomerous[1210].

8. TRICHOPTERA[1211] Kirby (_Synistata_ F. _Neuroptera_ Latr.). MM. Latreille and MacLeay are of opinion that _Semblis_ F. and _Phryganea_ L. ought to be associated in the _same_ group; and the latter gentleman has backed his opinion by some apparently cogent arguments[1212]: there are others, however, that seem to me more cogent, for considering them as belonging to _different_ Orders. Whoever examines the several tribes into which Mr. MacLeay has divided the _Neuroptera_, will observe in all of them a distinct _prothorax_, a circumstance which they possess in common with those Orders that use their mandibles for _mastication_; whereas in those that do _not_ use them for mastication, as the _Hymenoptera_, or that take their food by suction, this part is replaced by a mostly narrow collar, forming a part of the alitrunk[1213]. The existence then of the _prothorax_ in the _Perlidæ_, and of the _collar_ in the _Trichoptera_, affords no slight presumptive evidence that they belong to different Orders. Another circumstance that weighs much with me is, that the type of the neuration of the wings in _Perla_ is taken from the _Neuroptera_, in the _Trichoptera_ from the _Lepidoptera_; the same observation extends to the legs of both[1214], and likewise to the abdomen. Even in their oral organs, as far at least as relates to their mandibles, those of _Perla_, though membranaceous--a circumstance occurring even in _Coleoptera_--are of a Neuropterous type; while the angular termination of the cheeks in the _Phryganeæ_ approaches to the Lepidopterous mandibular rudiments. The principal argument on which Mr. MacLeay's opinion seems to rest, is, that the larvæ of both are aquatic, and clothe themselves in cases formed of various materials: but though this circumstance shows that they approximate in the system, it does not prove that they belong to the same order, since the general habit and appearance of the two animals when arrived at perfection contravenes it. The larvæ of _Myrmeleon_ and of _Leptis Vermileo_ form pitfalls of sand for their prey, and when they become pupæ, cover themselves with it[1215]; but this in them does not even prove an affinity, but only an analogy. The larva of _Perla_ is carnivorous[1216], that of _Phryganea_ mostly herbivorous[1217]: so that they are not precisely similar in their habits. Whether they resemble each other _altogether_, in their form, does not clearly appear. The above reasons will, I trust, justify me for considering them _at present_ as belonging to different Orders; but if further discoveries should confirm the opinion Mr. MacLeay espouses, I shall have no hesitation in yielding to it.

DEF. _Metamorphosis_ incomplete[1218].

_Mouth_ emandibulate.

_Prothorax_ replaced by a collar.

_Wings_ four, upper pair mostly hairy, lower ample, folded: _neuration_ branching.

_Anus_ without setæ. _Eggs_ extruded in a gelatinous mass[1219].

9. LEPIDOPTERA[1220] (_Glossata_ F.). Concerning this Order, no difference of opinion exists amongst Entomologists. Besides the scales that cover their wings, they are distinguished by the peculiar instrument of suction formerly described: neither of these characters, however, is perfectly universal; some of the Order (_Nudaria_) having no scales upon their wings, and others being without any _antlia_ (_Aglossa_). Other peculiar characters are to be found in them; for instance, the _patagia_, or tippets, that adorn their evanescent thorax[1221], and the _tegulæ_, or base-covers, of a shape quite dissimilar to those of _Hymenoptera_, which cover and defend the base of their wings[1222]. As in the last Order, their legs are located all together with scarcely any space intervening between them; and they often agree also in their spurs.

DEF. _Metamorphosis_ obtected[1223].

_Mouth_ antliate[1224].

_Prothorax_ very short, covered by a pair of tippets.

_Wings_ four, covered partially or generally with minute scales: _neuration_ branching, often with a central areolet.

10. DIPTERA[1225] (_Antliata_ F.). This Order likewise appears indebted for its name to the philosopher of Stagyra, who distinguishes the members of it from their counter-parts--the _Hymenoptera_--by their having an _oral_, while these have an _anal_ sting[1226]: and we may add, that while the last, on account of their wonderful economy and the benefits which by them PROVIDENCE confers upon mankind, have been justly regarded as the _princes_ of the winged insect world,--the former, when we consider the filthy and disgusting habits of their grubs, and the annoyance, both from their numbers and incessant assaults, of them, in their fly-state, may very properly be considered as its _canaille_. Almost all the tribes of _Hymenoptera_, from the saw-flies to the ants, have their representatives in this Order. Though the number of wings is its prominent feature, yet there are two-winged insects in other Orders, as some _Ephemeræ_: and the _Eproboscidea_ of Latreille seem rather a kind of winged _Aptera_, if we consider their _trophi_, than real _Diptera_; or they may form an osculant group,

## partly winged and partly apterous, between the two. I have before

remarked, that though, apparently, the insects of this Order have only _two_ wings, yet the under or secondary wings of the other Orders have in them their representative[1227]. Their poisers also, I formerly observed to you, are probably more connected with their respiration than with their flight[1228].

DEF. _Metamorphosis_ incomplete, or coarctate.

_Mouth_ proboscidate[1229].

_Prothorax_ replaced by a collar. _Sutures_ of the trunk mostly spurious[1230].

_Wings_ two, with winglets attached to them: _neuration_ various[1231]. _Poisers._

_Tarsi_ pentamerous.

_Ovipositor_ various[1232].

11. APHANIPTERA[1233] (_Aptera_ L. Lamarck. _Rhyngota_ F. _Suctoria_ Latr.) This is an osculant Order, and is distinguished from the other _Aptera_ L. in undergoing a regular metamorphosis. The larva is vermiform, the pupa incomplete, and inclosed in a cocoon. Probably the common flea and the chigoe would form distinct genera. The number of species of fleas is greater than has been supposed. I have been informed that Dr. Leach is acquainted with fourteen British species alone. Besides their metamorphosis, they are distinguished from the _Aptera_ by the number of segments into which their body is divided, and by their pentamerous tarsi. Something like elytra and a scutellum appear to distinguish these insects.

DEF. _Metamorphosis_ incomplete.

_Body_ apterous, compressed.

_Mouth_ rostrulate[1234].

_Tarsi_ pentamerous.

We are now come to those insects which, though they change their skin in their progress to their state of perfection, and some of them, as we have seen[1235], gain additional segments and pairs of legs, yet none of them acquire wings or wing-cases: these I have considered as forming one Order, under the denomination of

12. APTERA[1236] (_Synistata_, _Antliata_, _Unogata_, _Mitosata_ F.). I do not give this as a _natural_ Order. Our knowledge, however, of the internal organization of its groups, is not at present sufficiently matured to warrant the formation of them into new _Classes_[1237]: till that is more fully ascertained, it seems to me therefore best to consider these groups as forming three _Suborders_: the _first_ consisting of the _Hexapods_; the _second_ of the _Octopods_; and the _third_ of the _Polypods_. It will be better, I think, instead of giving a general character of the Order,--which principally consists in the insects composing it being _Apterous_, or never acquiring organs of flight,--to define each of these groups.

_Hexapods_ (_Ametabolia_ Leach, _Ametabola_ M^cL.). _Six_ legs may be regarded as the natural number in _all_ the insect tribes[1238]: but our business now is with those _Aptera_ whose body consists of _three_ greater segments, and which in none of their states have ever more or less than _six_ legs, and consist of the three Linnean genera _Pediculus_, _Lepisma_, and _Podura_ (_Thysanura_ and _Anoplura_). Some of the mites (_Acarus_ L.) are hexapods, but their body has no distinction of head, trunk, and abdomen. The metamorphosis of most female _Blattæ_, and of some other _Orthoptera_ that are apterous, cannot be regarded as materially different from that of the Hexapods. Amongst the _Anoplura_,--the _Pediculi_, or lice, are suctorious, and the _Nirmi_, or bird-lice, masticators,--a circumstance which in them does not appear to indicate even a different Order, and proves that undue stress ought not to be laid, independently of general characters, on the mode in which insects take their food.

DEF. _Metamorphosis_ complete.

_Body_ consisting of three principal segments.

_Mouth_ perfect, or rostellate[1239].

_Antennæ_ distinct.

_Legs_ six, in every state.

_Octopods._ This suborder consists of the _Trachean Arachnida_ of Latreille, excluding the _Pycnogonida_; of the _Acaridea_, _Sironidea_, _Phalangidea_, and part of the _Scorpionidea_ of Mr. MacLeay, and, with some exceptions, of the Linnean genera _Acarus_ and _Phalangium_. This last tribe (for with Linné, I include _Chelifer_ and _Obsidium_ in the _Phalangidea_,) on one side approaches _Scorpio_ by _Thelyphonus_, and on the other the _Aranidea_ by _Gonyleptes_; or, according to Mr. MacLeay, the transit is to both by _Galeodes_[1240]. But as there is reason for thinking that this last belongs to the _Pulmonary Arachnida_[1241], and forms a peculiar type in that Class, I consider the transit from the one to the other as above stated. The folded abdomen of _Gonyleptes_ seems much to correspond with that of the _cancriform_ spiders (_Carkinodes cancriformis_, &c.).

DEF. _Metamorphosis_ complete.

_Body_ consisting of one or two principal segments.

_Mouth_ various[1242].

_Antennæ_ obsolete, or represented by mandibles.

_Legs_ mostly eight, but in a few six only[1243].

_Polypods._ This suborder consists of Dr. Leach's Class _Myriapoda_, or the _Chilognatha_ and _Chilopoda_ of Latreille, corresponding with the Linnean genera _Iulus_ and _Scolopendra_. Mr. MacLeay has arranged them in the same Class with the Hexapods, and connects them with the _Anoplura_ by means of certain intestinal worms of an indistinct annulose structure[1244] (_Entozoa Nematoidea_ Rud.), in which the sexes are diœcious, and some of which are furnished with lateral spinulæ,--thus, as he supposes, connected with the Polypods; and with the _Anoplura_ by others (_Epizoaria_ Lam.) in which appendages appear somewhat analogous to the legs of Hexapods, as in _Cecrops_ Leach, and which like them are parasitic animals[1245]. But the right of these worms to be considered as members of the same Class with the Hexapods and Polypods at present appears rather problematical, and requires further examination.

DEF. _Metamorphosis_ subcomplete[1246].

_Body_ consisting of numerous segments.

_Mouth_ perfect[1247].

_Eyes_ compound or aggregate.

_Antennæ_ distinct.

_Legs_ six on the trunk, many on the abdomen.

I must next say something on the Orders of the _Arachnida_. Every one, at first sight, sees that _spiders_ and _scorpions_ are separated by characters so strongly marked, that they look rather like animals belonging to different Classes than to the same: these form the two _primary_ Orders of the _Arachnida_, and they appear to be connected by two _secondary_ or osculant ones,--on the one side by _Galeodes_, and on the other by _Thelyphonus_ and _Phrynus_[1248]. This Class, although there is an appearance of eight legs, is, strictly speaking, of a _Hexapod_ type; for the anterior pair, ordinarily regarded as legs and performing their function, are really the analogues of the maxillary palpi of perfect insects. This will be evident to you if you examine any species of _Galeodes_. These animals, if we look at them cursorily, we should regard as _Decapods_; but when we trace the two anterior pairs of apparent legs to their insertion, we find that both proceed from the _head_, which in that genus is distinct from the trunk; while the three last pairs, which alone are furnished with claws, are planted, as legs usually are, in the latter part. The first pair represent the ordinary palpi of _Arachnida_, are analogous to the labial ones of Hexapods, and, as likewise in _Phrynus_ and _Thelyphonus_, are more robust than what are usually taken for the first pair of legs; but they differ in being considerably longer, and instead of terminating in a _chela_ are furnished with a retractile sucker[1249]. The second pair are more slender and shorter than the first; they correspond precisely with what are deemed the first pair of legs of _Octopods_ and _Arachnida_, and are clearly analogous to the maxillary palpi of perfect insects. Whether the base of the first pair of these palpi is in any respect analogous to the labium of insects, (as that of the second seems to be to their maxillæ,) I am not prepared to assert: it will therefore be most advisable to name these palpi _anterior_ and _posterior_: but as they evidently proceed from the _head_ in _Galeodes_, and in that genus are clearly analogous to those of the _Phrynidea_, (which in their turn as clearly represent those of the _Aranidea_,) it follows that in all they are organs of the part representing the _head_, and therefore not in a _primary_ sense _legs_; although in a _secondary_, as M. Savigny has proved, they may be so called[1250].

1. ARANEIDEA M^cL. (_Aranea_ L., _Araneidæ_ Latr.) The _Araneidea_, or spiders, seem resolvable into _two_ suborders,--the _Sedentaries_ and the _Wanderers_; thus forming, perhaps, what Mr. MacLeay would denominate the normal groups of a circle of _Arachnida_.

DEF. _Mandibles_ armed with a perforated claw.

_Head_ and _Trunk_ coalite.

_Palpi_ pediform, anterior pair without claws.

_Abdomen_ without segments or elongated tail.

_Spiracles_ two[1251].

_Anus_ furnished with an apparatus for spinning[1252].

2. SCORPIONIDEA M^cL. (_Scorpio_ L. Latr.)

DEF. _Mandibles_ chelate.

_Head_ and _Trunk_ coalite.

_Anterior Palpi_ chelate[1253].

_Posterior Palpi_ pediform.

_Pectens_ two[1254].

_Abdomen_ divided into segments and terminating in a jointed tail, armed at the end with a sting[1255].

_Spiracles_ four pairs.

3. GALEODEA.

DEF. _Head_ distinct[1256].

_Eyes_ two.

_Mandibles_ chelate with dentated chelæ.

_Palpi_ pediform, the anterior pair thickest with a retractile sucker.

_Trunk_ consisting of two principal segments, with a minute supplementary posterior one[1257].

_Spiracles_ two placed in the trunk[1258].

_Pseudo-pectens_ two[1259].

_Abdomen_ divided into segments.

_Anus_ unarmed and without a spinning apparatus[1260].

4. PHRYNIDEA.

DEF. _Mandibles_ unguiculate.

_Anterior Palpi_ chelate or unguiculate[1261], very robust.

_Posterior Palpi_ pediform, very long and slender.

_Abdomen_ divided into segments.

_Spiracles_ two pairs.

_Anus_ terminating in a mucro, and sometimes in a filiform jointed tail without a sting at the end.

v. Having considered the _Orders_ into which _Insecta_ and _Arachnida_ may be divided, I am next to give you some account of the _groups_ into which each is further resolvable. To draw out, however, a complete scheme of these would be deviating from my province, and extend this letter to an enormous length. Indeed, to give the _natural_ primary and subordinate sections of every Order, would require a knowledge of the subject to which no Entomologist has yet attained. I shall therefore only say something general upon them, and refer you to an example of each kind of group.

Previously to the groups themselves their _nomenclature_ claims our attention. M. Latreille in his last arrangement of _Annulose_ animals has divided his Orders into _Sections_; _Families_; _Tribes_; and _Genera_: his tribes he has often further subdivided into lesser sections, represented by capital and small letters, &c.[1262]. Mr. MacLeay, discarding the term section, has _Tribes_; _Races_ (_Stirps_); _Families_; _Genera_, and _Subgenera_[1263]. But as in descending from the _Order_ to the lowest term, or the _species_, a series of groups gradually diminishing in value, which require a greater number of denominations than have yet been employed by Entomologists, often occur, I think we may with benefit to the science add to the list. I would therefore propose the following primary and subordinate divisions of an Order: 1. _Suborder_; 2. _Section_; 3. _Subsection_; 4. _Tribe_; 5. _Subtribe_; 6. _Stirps_; 7. _Family_; 8. _Genus_; 9. _Subgenus_. I would further propose that each of these successive groups should have a name always terminating alike, so that the value of the group when spoken of might always be known by the termination:--thus if a subclass end in _ata_, a suborder might end in _ita_; a section in _ana_, a subsection in _ena_; a tribe in _ina_, a subtribe in _ona_; a stirps in _una_; and a family in _idæ_; the genera being left free.