Читать книгу A Text-book of Entomology - A. S. Packard - Страница 24

The antennæ.—These are organs of tactile sense, but also bear olfactory, and in some cases auditory organs; they are usually inserted between or in front of the eyes, and moved by two small muscles at the base, within the head. In the more generalized insects the antennæ are simple, many-jointed appendages, the joints being equal in size and shape. The antennæ articulate with the head by a ball and socket joint, the part on which it moves being called the torulus (Fig. 32, r). In the more specialized forms it is divided into the scape, the pedicel, and a flagellum (or clavola); but usually, as in ants, wasps, and bees, there are two parts, the basal three-jointed one being the scape, and the distal one, the usually long filiform flagellum. The antennæ, especially the flagellum, vary greatly in form in insects of different families and orders, this variation being the result of adaptation to their peculiar surroundings and habits. The number of antennal joints may be one (Articerus, a clavigerid beetle), or two in Paussus and in Adranes cœcus (Fig. 43¹²), where they are short and club-shaped; in flies (Muscidæ, etc.), they are very short and with few joints, and when at rest lying in a cavity adapted for their reception. In the lamellicorn beetles the flagellum is divided into several leaves, and this condition may be approached in the serrate or flabellicorn antennæ of other beetles. In Lepidoptera, and in certain saw-flies and beetles, they are either pectinate or bipectinate, being in one case at least, that of the Australian Hepialid (Abantiades argenteus), tripectinate (Fig. 44), and in the dipterous (Tachinid) genus Talarocera the third joint is bipectinate (Fig. 45). In Xenos and in Parnus they may be deeply forked, while in Otiocerus, two long processes arise from the base, giving it a trifid shape. In dragon-flies and cicadæ, they are minute and hair-like, though jointed, while in the larvæ of many metabolous insects they are reduced to minute three-jointed tubercles. In aquatic beetles, bugs, etc., the antennæ are short, and often, when at rest, bent close to the body, as long antennæ would impede their progress.

Fig. 43.—Different forms of antennæ of beetles: 1, serrate; 2, pectinate; 3, capitate (and also geniculate); 4–7, clavate; 8, 9, lamellate; 10, serrate (Dorcatoma); 11, irregular (Gyrinus); 12, two-jointed antenna of Adranes cæcus.—After LeConte. a, first joint of flagellum of antenna of Troctes silvarum; b, of T. divinatorius.—After Kolbe.

Fig. 44.—Tripectinate antenna of an Australian moth.

While usually more or less sensorial in function, Graber states that the longicorn beetles in walking along a slender twig use their antennæ as a rope-dancer does his balancing pole.

Fig. 45.—Antenna of Talarocera nigripennis, ♂.—After Williston.

Recent examination of the sense-organs in the antennæ of an ant, wasp, or bee enables us, he says, to realize what wonderful organs the antennæ are. In such insects we have a rod-like tube which can be folded up or extended out into space, containing the antennal nerve, which arises directly from the brain and sends a branch to each of the thousands of olfactory pits or pegs which stud its surface. The antenna is thus a wonderfully complex organ, and the insect must be far more sensitive to movements of the air, to odors, wave-sounds, and light-waves, than any of the vertebrate animals.

That ants appear to communicate with each other, apparently talking with their antennæ, shows the highly sensitive nature of these appendages. “The honey-bee when constructing its cells ascertains their proper direction and size by means of the extremities of these organs.” (Newport.)

How dependent insects are upon their antennæ is seen when we cut them off. The insect is at once seriously affected, its central nervous system receiving a great shock, while it gives no such sign of distress and loss of mental power when we remove the palpi or legs. On depriving a bee of its antennæ, it falls helpless and partially paralyzed to the earth, is unable at first to walk, but on partly recovering the use of its limbs, it still has lost the power of coördinating its movements, nor can it sting; in a few minutes, however, it becomes able to feebly walk a few steps, but it remains over an hour nearly motionless. Other insects after similar treatment are not so deeply affected, though bees, wasps, ants, moths, certain beetles, and dragon-flies are at first more or less stunned and confused.

The antennæ afford salient secondary sexual differences, as seen in the broadly pectinated antennæ of male bombycine moths, certain saw-flies (Lophyrus), and many other insects.

The mouth-parts, buccal appendages, or trophi, comprise, besides the labrum, the mandibles and maxillæ.

The mandibles.—These are true jaws, adapted for cutting, tearing, or crushing the food, or for defence, while in the bees they are used as tools for modelling in wax, and in Cetonia, etc., as a brush for collecting pollen. They are usually opposed to each other at the tips, but in many carnivorous forms their tips cross each other like shears. They are situated below the clypeus on each side, and are hinged to the head by a true ginglymus articulation, consisting of two condyles or tubercles to which muscles are attached, the principal ones being the flexor and great extensor (Fig. 48). They are solid, chitinous, of varied shapes, and in the form of the teeth those of the same pair differ somewhat from each other (Fig. 46 A). In the pollen-eating beetles (Cetoniæ) and in the dung-beetles (Aphodius, etc.) the edge is soft and flexible. In the males of Lucanus, etc. (Fig. 47), and of Corydalus (Fig. 29), they are of colossal size, and are large and sabre-shaped in the larvæ of water-beetles, ant-lions, Chrysopa, etc. where they are perforated at the tips, through which the blood of their prey is sucked.

While the mandibles are generally regarded as composed of a single piece, in Campodea and Machilis there appears to be an additional basal piece apparently corresponding to the stipes of the first maxilla, and separated by a faint suture from the molar or distal joint. In Campodea there is a minute movable appendage figured both by Meinert and by Nassonow, which appears to represent the lacinia of the maxilla (Fig. 48). Wood-Mason has observed in the mandibles of the embryo of a Javanese cockroach, Blatta (Panesthia) javanica, indications of “the same number of joints as in that of chilognathous myriopods, or one less than in that of Machilis.” Also he adds: “In both ‘larvæ’ and adults of Panesthia javanica a faint groove crosses the ‘back’ of the mandible at the base. This groove appears to be the remains of the joint between the third and apical segments of the formerly 4–segmented mandibles.”

Fig. 46.—Various forms of mandibles. A, right and left of Termopsis. A′, showing at the shaded portion the “molar” of Smith. B, Termes flavipes, soldier; md, its mandible. C, Panorpa.

Fig. 47.—Chiasognathus grantii, reduced. Male.—After Darwin.

Fig. 48.—Mandible of Campodea: l, prostheca or lacinia; g, galea; f, f, flexor muscles; e, extensor; r, r, retractor; rt, muscle retaining the mandible in its place.—After Meinert. A, extremity of the same.—After Nassonow.

Fig. 49.—Mandible of Passalus cornutus with the prostheca (l): A, that of a Nicaraguan species; a, inside, b, outside view, with the muscle.

He also refers to the prostheca of Kirby and Spence (Fig. 49), which he thinks appears to be a mandibular lacinia homologous with it in Staphylinidæ and other beetles (J. B. Smith also considers it as “homologous to the lacinia of the maxilla”), and on examining it in P. cornutus and a Nicaragua species (Fig. 49), we adopt his view, since we have found that it is freely movable and attached by a tendon and muscle to the galea. In the rove beetles (Goërius, Staphylinus, etc.) and in the subaquatic Heteroceridæ, instead of a molar process, is a membranous setose appendage not unlike the coxal appendages of Scolopendrella, movably articulated to the jaw, which he thinks answers to the molar branch of the jaws in Blatta and Machilis. “It has its homologue in the diminutive Trichopterygidæ in the firmly chitinized quadrant-shaped second mandibular joint, which is used in a peculiar manner in crushing the food”; also in the movable tooth of the Passalidæ, and in the membranous inner lobe of the mandibles of the goliath-beetles, etc.

J. B. Smith has clearly shown that the mandibles are compound in certain of the lamellicorns. In Copris carolina (Fig. 50), he says, the small membranous mandibles are divided into a basal piece (basalis), the homologue of the stipes in the maxilla; another of the basal pieces he calls the molar, and this is the equivalent of the subgalea, while a third sclerite, only observed in Copris, is the conjunctivus, the lacinia (prostheca) being well developed. Smith therefore concludes “that the structure of the mandible is fundamentally the same as that of the labium and maxilla, and that we have an equally complex organ in point of origin. Its usual function, however, demands a powerful and solid structure, and the sclerites are in most instances as thoroughly chitinized and so closely united to the others that practically there is only a single piece, in which the homology is obscured.” (Trans. Amer. Ent. Soc., xix, pp. 84, 85. 1892.) From the studies of Smith and our observations on Staphylinus, Passalus, Phanæus, etc. (Fig. 50, A, B) we fully agree with the view that the mandibles are primarily 3–lobed appendages like the maxillæ. Nymphal Ephemerids have a lacinia-like process. (Heymons.)

Fig. 50.—Mandible of Copris carolina.—After Smith. A′C. anaglypticus. A (figure to right), do. of Leistotrophus cingulatus; B, of Phanæus carnifex; g′, end of galea,—g, enlarged; c, conjunctivus. C, of Meloë angusticollis: l, lacinia; a, lacinia enlarged.

Mandibles are wanting in the adults of the more specialized Lepidoptera, being vestigial in the most generalized forms (certain Tineina and Crambus), but well developed in that very primitive moth, Eriocephala (Fig. 51). They are also completely atrophied in the adult Trichoptera, though very large and functional in the pupa of these insects (Fig. 52), as also in the pupa of Micropteryx (Fig. 53). They are also wanting in the imago of male Diptera and in the females of all flies except Culicidæ and Tabanidæ.

They are said by Dr. Horn to be absent in the adult Platypsyllus castoris, though well developed in the larva; and functional mandibles are lacking in the Hemiptera.

The first maxillæ.—These highly differentiated appendages are inserted on the sides of the head just behind the mandibles and the mouth, and are divided into three lobes, or divisions, which are supported upon two, and sometimes three basal pieces, i.e. the basal joint or cardo, the second joint or stipes, with the palpifer, the latter present in Termitidæ (Fig. 54, plpgr), but not always separately developed (Fig. 55). The cardo varies in shape, but is more or less triangular and is usually wedged in between the submentum and mandible. It is succeeded by the stipes, which usually forms the support for the three lobes of the maxilla, and is more or less square in shape.

Fig. 51.—Mandible of Eriocephala calthella: a, a′, inner and outer articulation; s, cavity of the joint (acetabulum); A, end seen from one side of the cutting edge.—After Walter.

Fig. 52.—A, Pupa of Phryganea pilosa.—After Pictet. B, mandibles of pupa of Molanna angustata.—After Sharp.

Fig. 53.—Pupa of Micropteryx purpuriella, front view: md, mandibles; mx.p, maxillary palpus, end drawn separately; mx.’p, labial palpi; lb, labrum; A, another view from a cast skin.

The three distal divisions of the maxilla are called, respectively, beginning with the innermost, the lacinia, galea, and palpifer, the latter being a lobe or segment bearing the palpus. The lacinia is more or less jaw-like and armed on the inner edge with either flexible or stiff bristles, spines, or teeth, which are very variable in shape and are of use as stiff brushes in pollen-eating beetles, etc. The galea is either single-jointed and helmet-shaped or subspatulate, as in most Orthoptera, or 2–jointed in Gryllotalpa, or lacinia-like in Myrmeleon (Fig. 55, C); or, in the Carabidæ (Fig. 56) and Cicindelidæ, it is 2–jointed and in form and function like a palpus.

Fig. 54.—A, maxilla of Termopsis angusticollis. B, Termes flavipes: c, cardo; sti, stipes; plpgr, palpiger; palp, palpus; lac, lacinia; g, gal, galea.

Fig. 55.—A, maxilla of Mantispa brunnea. B, Ascalaphus longicornis. C, Myrmeleon diversum. Lettering as in Fig. 54.

Fig. 56.—Maxilla of a carabid, Anophthalmus tellkampfii: l, lacinia; g, 2–jointed galea; p, palpus; st, stipes; c, cardo.