CHAPTER XX.

Functions and Instincts. Insect Condylopes.

THE animals of the class we are next to consider, have been regarded by many modern zoologists, especially of the French, school, as inferior both to Crustaceans and Arachnidans, on account of their having only, as it were, a rudimental heart, exhibiting indeed a kind of systole and diastole, but unaccompanied by any system of vessels by which the blood might circulate in them. A learned and acute writer, and eminent zoologist, amongst our own countrymen, has with great force controverted the justice of this sentence of degradation pronounced upon Insects; an opinion which has also been embraced by many other modern writers on the subject, and considerable doubt has been shown to rest upon the main foundations upon which the illustrious and lamented Baron Cuvier, who was the father of the hypothesis, had built it.1

But the important discoveries of Dr. Carus, who first proved that a circulation really exists in various larves of Insects, and afterwards that it is also discoverable in several perfect ones," have placed the matter beyond all doubt. Taking, therefore, into consideration the nervous system of Insects, as well as those of circulation and respiration, as ought, in all reason, to be done -for upon comparison of these three systems so intimately connected with life and sensation, surely the first place is due to that by which alone the animal is conscious of its existence and that of the world it inhabits, and is enabled to run the race appointed by its Creator; surely if even no Carus had appeared to demonstrate the existence of a circulation in these animals, still the perfection of their nervous system, compared with that of the Molluscans, in determining their respective stations, would be a sufficient counterpoise to a heart and vascular system for circulation; and if to this superiority we add

1 Mac Leay, Hor. Entomolog. 204, 297.

2 Introd. to Comp. Anat. E. T. by Gore, ii. 392. Act. Acad. Cæs Nat. Cur, xv. ii.

1

the number and nature of the several organs by which this system acts, and the fruits of such agency in the activity and various instincts of the animals endowed with it, embodying the moving will, the informing sense, the impelling appetite, compared with the inertness and sluggish motions, and apathetic existence, and paucity of instinctive actions in the great majority of the Molluscans,-who is there that will hesitate to conclude that he who created the Insect world, gifted them with so many and such wonderful instincts, inspired them with such incessant activity, fitted them with such various organs for such a diversity of locomotions under the earth, on the earth, in the air and in the water, meant to place them far above the headless Oyster, with scarcely any organs of sensation, and scarcely any motion but that of opening and shutting its shell, or even than the Cuttle-fish, though furnished with eyes, and even three hearts, and a very extraordinary animal, yet destitute of many organs of the senses and of locomotion found in Insects, and most of those that they have not formed upon the plan of the higher animals, but rather borrowed from the confessedly lower Classes of Polypes and Radiaries?1

With regard to the Crustaceans and Arachnidans, setting aside the superiority of Insects in their instincts, the single circumstance of the reproduction of mutilated organs in the former seems to prove an inferiority of rank and a tendency towards the Polype.

When we consider attentively these little beings, the infinite variety of their forms, the multiplicity and diversity of their organs, whether of sense or motion, of offence or defence, for mastication or suction; or those constructed with a view to their several instincts, and the exercise of those functions devolved upon them by the wisdom of their Creator; the different kinds also of sculpture which is the distinction of one tribe, and of painting, which ornaments another, the brilliant colours, the metallic lustre, the shining gold and silver with which a liberal and powerful hand has invested or bespangled numbers of them; the down, the hair, the wool, the scales, with which He, who careth for the smallest and seemingly most insignificant works of his hand, hath clothed and covered them; when all these things strike upon our senses, and become the subject of our thoughts and reflection, we find a scene passing before us far exceeding any, or all of those, that we have hitherto contemplated in our progress from the lowest towards the highest members of the animal kingdom, and which for its

1 See above, p. 163.

2 Mac Leay, Hor. Ent. 206, 298.

extent, and the myriads of its mustered armies, each corps distinguished as it were by its own banner, and under its proper leaders, infinitely outnumbers all the members of the higher Classes, which stand as it were between aquatic and terrestrial animals, many of its tribes under one form inhabiting the water, and under another the earth and the air.

The following characters distinguish this great Class:

BODY, covered with a horny or coriaceous integument. Spi. nal chord knotty, terminating anteriorly in a bilobed brain; a heart and imperfect circulation, sometimes vascular, and sometimes extra-vascular; respiration by trachea, receiving the air by spiracles; legs jointed, in the perfect insect always six.

The Class of Insects may be divided into two Sub-classes,1 viz. Ametabolians, or those that do not undergo any metamorphosis, and have no wings; and Metabolians, or those that undergo a metamorphosis, and are usually fitted with wings in

their final state.

Sub-class 1.-Ametabolians are further subdivided into two Orders, Thysanurans and Parasites.

Order 1.-The Thysanurans are remarkable for their anal appendages, which consist either of jointed organs resembling antennæ, and approaching very near to the caudal organs of the cockroach, the use of which is not certainly known; or of an inflexed elastic caudal fork bent under the abdomen, which enables them to leap with great agility. To the first of these tribes belongs the common sugar-louse, and to the last the spring-tails.

It must be observed, however, that this is not a natural Order, for there is no analogy between the jointed tails of the sugar-louse, which some have supposed to belong or approach to the Orthoptera, and the unjointed leaping organ of the springtail. The latter animals, indeed, seem to form an osculant tribe, without the pale of the Class of Insects, and perhaps having some reference to the Chilopodans amongst the Myriapods, with which they agree, in having only simple eyes, like spiders, on each side of the head. Those of the spring-tails consist of eight such eyes, arranged in a double series, and planted in an oval space, in shape resembling an Insect's eye. The Chilopodans have only four on each side. The Insects of this Order probably feed upon detritus, whether animal or

1 See above, p. 198. 3 Lepisma.

2 Blatta.

4 Podura. Sminthurus.

vegetable, their masticating organs being very weak, and fitted to comminute only putrescent substances.

Order 2.-The Order of Parasites-consisting of the most unclean and disgusting animals of the whole Class, infest both man, beast, and bird, and no less than four1 species accounted by Linné, &c. as varieties, being attached to the former-may be divided into two sections, those that live by suction, and those that masticate their food. To the first of these helong the human and the dog-louse, and to the other the various lice that inhabit the birds, of which almost every species has a peculiar one.

I have, on a former occasion, alluded to the Order of Parasites, when speaking of punitive animals: here I must observe, that like other instruments employed by God to visit the sins of mankind, they are intended to produce a sanative effect, as well as to punish. It is generally known that they abound only on those whose habits are dirty, in whom they may prevent the diseases which such habits would otherwise generate, as well as stimulate them to greater attention to personal cleanliness. The bird-louse is probably useful to birds in devouring the sordes which must accumulate at the root of their plumes.

Sub-class 2.-Metabolians, by most modern writers on Insects, are considered, from their oral organs, as constituting two Sections, which are denominated Haustellate and Mandibulate Insects. I may here observe that the instrument of suction in a Haustellate mouth consists of pieces, though differently circumstanced, precisely analogous to those employed in mastication in a Mandibulate one, which has been most satisfactorily demonstrated, and with great elegance, by M. Savigny, in the first part of his Animaux sans Vertèbres.5

As there are several Orders called Osculant, that are intermediate between these Sections, I shall arrange the whole in three columns.

OSCULANT ORDERS.

1. Aphaniptera. 2. Homaloptera. 3. Trichoptera. 4. Dermaptera. 5. Strepsiptera.

1 Pediculus, Capitis, Corporis, Nigritarum, and Phthirus Pubis.

2

Nirmus.

4 Ibid, p. 253.

3 See above, p. 7. See Introd, to Ent. i. 83.

With regard to the characters of these Orders:

Order 1.-The Aphaniptera (Flea, Chigoe) are apterous and parasitic, but differ from the Order of Parasites by undergoing a metamorphosis. They connect the Suctorious Parasites with the Diptera.

Order 2.-The Homaloptera (Forest-fly, &c.) called also Pupipara, because their eggs are hatched in the matrix of the mother, where they pass their larve state, and are not excluded till they have become pupes. Most of them have two wings, but one genus is apterous:1 these seem intermediate between certain Acaridans, as the bat-mite, and the Diptera; they seem also, in some respects, to connect with the Arachnidans, whence they have been called spider-flies.

Order 3.-The Trichoptera (Caseworm-flies) have four hairy membranous wings, in their nervures resembling those of Lepidoptera, the under ones folding longitudinally. The mouth has four palpi, but the masticating organs are merely rudimental. Their place seems to be somewhere between the saw-flies and those moths whose caterpillars clothe themselves with different substances.

Order 4.-The Dermaptera (Earwigs) have two elytra and two wings of membrane, folded longitudinally, and their tail is armed with a forceps. They appear to be between the Coleoptera and Orthoptera.

Order 5.-The Strepsiptera (Wild bee-fly, Wasp-fly), parasitic animals, that have two ample wings, forming the quadrant of a circle, and of a substance between coriaceous and membranous, and two elytriform subspiral organs, appendages of the base of the anterior legs. Their place is uncertain, some placing them between the Coleoptera and Dermaptera ; and others between the Lepidoptera and Diptera.

Order 6.-The Diptera (Two-winged Flies and Gnats, &c.), as their name indicates, have only two membranous wings, usually accompanied by two winglets, representing the under wings of the Tetrapterous Orders, and two poisers, which appear connected with a spiracle.

1 Melophagus, The Sheep-louse.