The system here stated, of naming and characterizing larvæ from the resemblance and analogy, in many cases very striking, that they bear to the apterous tribes, is a very happy and original one, and does its author great credit; yet I think in some instances, as I shall soon have occasion to point out to you, the application of it is not so happy as the first idea. But this is always the case when a new law of nature is discovered; the proper application of it is gradually developed, and it does not at all detract from the merit of the first discoverer, that all the bearings of such law do not strike him as it were intuitively.
Having, however, got the vantage-ground afforded by this discovery of my friend, let us see if by standing upon it we cannot get a tolerable generalization of the larvæ of all orders of insects that undergo a metamorphosis. But first I must observe, that as in the perfect animals, so in their larvæ, the different groups are connected by certain transition species, exhibiting characters common to two or more of them; and likewise that in many cases, which you will see as we proceed, the analogy is as strong or stronger between them and the Crustacea (and in a few instances Arachnida, and even Mollusca) than the Ametabola. My denominations, therefore, will be taken from those tribes where the analogy appears to me the most striking, and not from the Ametabola alone.
I shall begin by drawing up for you a list of the Primary forms that I seem to have observed, and their characters; and then going through the orders, shall give you the examples of each, with such observations upon them as the case may require.
Primary Forms of Larvæ.
| APTERA. | ARACHNIDA. | CRUSTACEA. | MOLLUSCA. |
| Anopluriform. | Araneidiform. | Isopodiform. | Limaciform. |
| Thysanuriform. | Onisciform. | ||
| Chilopodiform. | Idoteiform. | ||
| Chilognathiform. | Amphipodiform. | ANNELIDA. | |
| Stomapodiform. | Vermiform. | ||
| Decapodiform. | |||
| Branchiopodiform. |
Characters.
1. Anopluriform. Carnivorous; hexapod; antenniferous: with a shortish oblong depressed body, and distinct thoracic shield. Example: Psocus, Coccinella, most Hemiptera[380].
2. Thysanuriform. Polyphagous; hexapod; antenniferous: body with segments of trunk distinctly marked; anus often furnished with setæ or mucro. Ex. Meloe[381]? Thrips, Aphis.
3. Chilopodiform. Carnivorous; subhexapod; antenniferous: body depressed, elongate, linear, with falcate acute mandibles, a distinct thoracic shield, and an anal proleg. Ex. Cicindela[382]? Carabus L.
4. Chilognathiform. Herbivorous; body subcylindrical, elongate, linear; no thoracic shield; often many prolegs, sometimes a retractile one, and sometimes none.—Ex. Elater, Petalocera, most Lepidoptera, Tenthredo L.[383]
5. Vermiform. Polyphagous; apod or hexapod: with very short legs; antennæ nearly obsolete; body fleshy, plicate, with sides often plicato-papillose; no distinct thoracic shield. Ex. Curculio L., Cerambyx L., Musca L., and many other Diptera[384].
6. Araneidiform. Carnivorous; hexapod: body very short; mandibles long, suctorious; animal lying in wait for its prey in a pitfall it has prepared; motion retrogressive. Ex. Myrmeleon L.[385] Cicindela?
7. Isopodiform. Saprophagous; hexapod; antenniferous, with longer antennæ: body oblong; thoracic shield distinct; anus styliferous or laminiferous. Ex. Blatta L. Silpha L.?
8. Onisciform. Herbivorous; polypod; antenniferous: body short, oblong, depressed, margined. Ex. Erycina, Lycæna, in the Lepidoptera, and some species of Tenthredo L.[386]
9. Idoteiform. Subcortical; hexapod; antennæ obsolete: body much depressed, with the last segment elongate, terminating in three or more mucros. Ex. Larva from Brazil. Perfect insect at present unknown.
I have placed this larva, which was described above[387], amongst crustaceous forms, because of the remarkable resemblance which the last segment of the body bears to that of the Idoteidæ; but I do it with considerable hesitation, since in other respects its type seems to be in the Ametabola. In its want of antennæ, very short legs, and ventral asperities, it resembles some of the Vermiform larvæ; in its small head, distinct thoracic shield, and oblong shape, it approaches the Anopluriform; and in its very depressed body, but not at all in other respects, the Chilopodiform. At any rate, it appears of a primary Type.
10. Læmodipodiform. Herbivorous; hexapod; antenniferous, with long antennæ: body elongate, subcylindrical; second segment of the trunk the longest; anterior pair of legs distant from the other two. Ex. Phasma.
11. Amphipodiform. Herbivorous; hexapod; antenniferous, with long antennæ: body shortish, compressed, saltatorious. Ex. Gryllus L.[388]
12. Stomapodiform. Carnivorous or saprophagous; hexapod; antenniferous, with long antennæ: body elongate, subdepressed, with raptorious hands, and abdomen wider than the trunk; in aquatic species furnished with lateral gills. Ex. Mantis, Ephemera? Sialis?
13. Decapodiform. Carnivorous; hexapod; antenniferous: body elongate, narrow, convex, compressed, tapering towards the tail; tail with natatorious laminæ. Ex. Dytiscus L., Agrion F.[389]
14. Branchiopodiform. Carnivorous?; aquatic; apod; antenniferous: head distinct: body transparent, flexile, furnished with a respiratory tube just above the tail. Ex. Culex[390].
15. Limaciform. Herbivorous; apod, or with very short legs: body ovate or obovate, slimy. Ex. Apoda Haw., Tenthredo Cerasi L.