1. Spinneret (Fusulus). The organ which spins the silk. Plate [XXI]. Fig. 9.
2. Forcipate Lip (Labium Forcipatum). Mask of larvæ and pupæ of Libellulina[1122]. Plate [XVI]. Fig. 5. a. 3. Unguiform Mandibles (Mandibulæ unguiformes). The parallel claw-shaped mandibles of many Diptera. Plate [XX]. Fig. 1, 2. c´.
4. Prop (Ereisma). A bipartite retractile glutinous organ exerted from between the legs of the genus Sminthurus, and employed by the animal to support itself when its legs fail it[1123].
5. Fecifork (Fæcifurca). The anal fork on which the larva of Cassidæ, &c. carry their feces. Plate [XVIII]. Fig. 2. a.
6. Mastigia (Mastigia). Two anal organs in the larvæ of Cerura Vinula, exerting from their apex a retractile flexible thread, with which they endeavour, by lashing their sides, to drive away the Ichneumons. Plate [XIX]. Fig. 2. a.
7. Syringes (Syringia). Organs situated in various parts of larvæ, from which they ejaculate a watery fluid to annoy or drive away their enemies[1124].
8. Rumules (Rumulæ). Teat-like fleshy protuberances observable on the bodies of various larvæ[1125].
9. Aeriducts (Aëriductus). Respiratory organs often foliaceous, with which the sides of the abdomen, the tail, and sometimes the trunk of aquatic larvæ and pupæ are often furnished. Plate [XXIX]. Fig. 3-7.
10. Prolegs (Propedes). Fleshy exarticulate pediform often retractile organs, which assist various larvæ in walking and other motions, but which disappear in the perfect insect. Plate [XVIII]. Fig. 11, 12. b.
a. Coronate Prolegs (Propedes coronati). Prolegs that have an intire coronet of crotchets. Plate [XXIII]. Fig. 1.
b. Semicoronate Prolegs (Propedes semicoronati). Prolegs that have a semicoronet of crotchets.
c. Unarmed (Inermes). Prolegs that have no crotchets.
d. Stilt Prolegs (Propedes grabati). Prolegs that are unnaturally long, and elevate the animal. Plate [XXIII]. Fig. 7. a.
α. Coalite Stilt Prolegs (Propedes grabati coaliti). When stilt prolegs unite so as to form only one leg bifid at its apex. Plate [XXIII]. Fig. 7. b.
PUPÆ.
1. Adminicula (Adminicula). Semicoronets of minute teeth which arm the back of the abdomen of subterraneous pupæ, by which they are enabled to emerge from under the earth. Plate [XVI]. Fig. 13. e.
2. Cremastræ (Cremastræ). The anal hooks by which many pupæ suspend themselves. Plate [XXIII]. Fig. 8. a.
3. Cocoon (Folliculus). The silken case in which the pupæ of many insects are inclosed. Plate [XVII]. Fig. 5-8.
N.B. Other terms for Pupæ are explained Vol. III. p. [249].
[LETTER XLVII].
SYSTEM OF INSECTS.
Having considered insects as to their History, Anatomy and Physiology, we must next enter a new and ample field, in which, like most of our predecessors, we shall often be perplexed and bewildered by the infinite variety of devious paths which traverse it, and by the mazy labyrinths in which the more we wander the less ground we seem to gain.—You will easily perceive I am speaking of the System of Insects. System is a subject which has engaged the attention of Naturalists from the time of Aristotle to the present day; and even now that it has been so much and so ably discussed, they are far from being agreed concerning it. In our own country a clue has, however, of late been furnished, which upon the whole seems better calculated to enable us to thread the intricate labyrinth of nature, than any thing previously excogitated.
There are two words relating to this subject concerning which Naturalists seem not to have very precise ideas—Method and System. They have often been confounded and used indifferently to signify the same thing. Thus we hear of a Natural Method and a Natural System. Linné seems to have regarded the former of these terms as representing the actual disposition of objects in nature[1126], while by System he understands their classification and arrangement by Naturalists[1127]. But if we consider their real meaning,—a Method should signify an Artificial, and a System a Natural arrangement of objects[1128]. As many systematists, however, have aimed at giving a natural arrangement, though with various success,—some, as the French school, (to which we are principally indebted for the progress already made,) approximating nearer to the true idea than others,—and none having a perfect conception of it, of which probably in our present state, our minds, from its intricacy, are incapable,—it might perhaps be as well to call every arrangement whose object is confessedly artificial, a Method; and that which aims at the plan of nature, a System. Under this view system-makers would be divided into two classes,—the Methodists and Systematists.
The system of nature, which we are now to consider, may be viewed under a double aspect; for with regard to all created objects there is a System of Distribution, and a System of Correlation, which appear to be quite independent of each other. The former will best fall under our notice when we are treating of the Geography of insects: I shall therefore now confine myself to the latter.