Labrum

“ Eyes large, with coarse ommatidia. Labrum semicircular in outline, tumid. Labial lobes large, oval, contiguous with one another, at the tip of the labrum. Maxillary palpi moderately long and slender, nearly straight, gradually narrowed to the tip which ends opposite the knee-joint of the fore legs. Antennæ with the basal segments separated only by the cephalic crest, the sheaths ending about opposite or a little before the lateral angle of the thorax.
Pronotal breathing-horns (fig. 14) very small, almost microscopic; when viewed from the dorsal aspect appearing as tiny triangular tubercles. ”

“ As the labrum is formed of similar membrane with that of the succeeding segment of the body, its limit downward, beneath the knob, can be told only by a small apodeme which projects inwards, at a little distance within the line where the membrane of the body is reflexed upwards (c) , so as to form the inner tunic of the sack.
The mandibles, palpi, and maxillæ, all project more than is usual. The Palpi (f, fig. 9, 5) are narrow, flattened, and taper a little; they support a few long bristles on their tips, and on one of their sides. ”

“ The labrum, or upper lip, has a vertical motion, and when not in use falls over the organs beneath it; while it is covered, in its turn, by the mandibles, which are jointed on to the cheeks, and act laterally.
The pharynx is a cavity lying beneath the epipharynx, and can be closed by the latter, over which the two previously described parts lap, so that the entrance to the œsophagus is trebly protected. ”

“ Indeed the whole arrangement of the limbs of Apus with the sensory endites forms an excellent trap to catch prey over which the labrum has passed.
In alcoholic specimens of Apus the labrum is not in a horizontal plane, as it is in most well preserved trilobites, but is tipped down at an angle of from 30 to 45, and the big mandibles lie under it. It has considerable freedom of motion and is held in place by muscles which run forward and join the under side of the head near its posterior margin. ”

“ These three lips can be brought together, and form a valve. The lateral lips are very narrow at the mouth or rostral end of the orifice, where the hairy lancet-shaped crest of the labrum closes the orifice, and largely expand towards the posterior end: they are produced from the inner tunic of the sack: they appear formed of the finest hairs, placed parallel and approximate, but when examined under the highest powers, these hairs (for they still appear such) are found to be united by delicate membrane, which has its extreme edge fimbriated. ”

“ Alimentary Canal.—The mouth of the Phyllopoda is overhung by the large labrum, so that a kind of atrium is formed, outside the mouth itself, in which mastication is performed; numerous unicellular glands, opening on the oral face of the labrum, pour their secretion into the atrial chamber, and may be called salivary, though the nature of their secretion is not known. The mouth has commonly two swollen and setose 29lips, running longitudinally forwards from the bases of the first maxillae, and often wrapping round the blades of the mandibles. ”

“ The Labium, or lower lip, is situated below the proboscis and carries the Labial palpi (figs. 5 and 6) , two large jointed organs which are very conspicuous in nearly all the species and often quite conceal the maxillary palpi. They are usually regarded as organs of touch, but their true function does not seem to be properly understood. In the Lepidoptera they appear to protect the proboscis, which, when out of use, is always coiled up in a spiral between them. The labrum and mandibles can only be seen by removing the large labial palpi. ”

“ In fig. 4, the labrum, with the œsophagus, has been removed, whilst the two outer maxillæ, the right-hand inner maxilla and mandible (with the exterior and basal portions, d, d′′, of one palpus) are seen from the outside; but in order that these parts should all be shown, the whole of the right-hand side of the mouth has been spread out, for the teeth of the mandible should have stood in a vertical line between the two outer maxillæ. In the mandibles, the free upper part is separated, by a distinct articulation, from the square piece of thickened membrane (fig. 3, c1) on which it is supported ”

“ They are entertaining inmates of an aquarium; they play slowly up and down in the corners of the tank, exploring every angle and cranny, hanging in every possible attitude, especially at night. They soon be [Pg 201] come familiar, and may be preserved in health a long time. They are constantly occupied in searching for, and picking off atoms, invisible to us, with their protrusile lips. These organs are remarkably large, thick, and fleshy, whence has been derived the name of the family, Labridæ (from labrum, a lip) ; and, in death, they are generally projected in an uncouth and repulsive form. ”

“ APERTURE or MOUTH. The entrance to the spiral cavity of univalve shells. The parts of the aperture are separately described, as follows: The inner lip or labium is that part which lies over the preceding whorl of the shell. It terminates anteriorly, or towards the lower part in what is termed the columella, so called because it forms a kind of axis on which the volutions turn. The outer lip, sometimes called the labrum, is on the opposite side, or the farthest from the axis. If the edges of the inner and outer lips unite all round, they are described as composing the peritrême. In fig. ”

“ The inner fold of the labrum is much thickened, yellow, punctured, and with a tuft of fine bristles on each side.
Palpi, approaching each other but not touching, club-shaped, or with broad and square extremities, thickly fringed with serrated bristles. [Pg 312]
Mandibles with three unusually strong teeth, slightly graduated in size, with the inferior angle very coarsely pectinated; the lower edges of the main teeth are roughened.
Maxillæ, (Pl. X. fig. 13) . Spinose edge about half the length of the mandibles; the two upper spines are unusually strong ”

“ The prolongation of the lower lip or labium into a prominent proboscis, which in the female sex contains the full complement of piercing organs found in blood-sucking Diptera, namely paired mandibles, paired maxillae, a tubular hypopharynx (the common outlet of the salivary glands) , and an upper lip or labrum. (2) The presence of variously formed scales on the body and its appendages: the head is clothed with scales, the thorax with hairs or scales, and the abdomen with either hairs or scales, or both ”

“ Fig. 63.—Selandria larva, common on Carya porcina, with details of mouth-parts: leg, leg; mx, maxilla; gal, galea; lac, lacinia.
The second maxillæ.—The “under-lip” or labium of insects is formed by the fusion at the basal portion of what in the embryo are separate appendages, and which arise in the same manner as the first maxillæ. They are invariably solidly united, no cases of partial or incomplete fusion being known. The so-called labium is situated in front of the gula or gular region, and is bounded on each side by the gena, or cheek. ”

“ The delicate tunic lining the sack, (a mere duplicature of that thick one, forming the outside of the capitulum, and generally transformed into valves,) and the integuments of the whole body, are regularly moulted. With these integuments, the membrane lining the œsophagus, the rectum, and the deep olfactory pouches, and the horny apodemes of the maxillæ, are all cast together. I have seen a specimen of Lepas, in which, from some morbid adhesion, the old membrane lining one of the olfactory pouches had not been moulted, but remained projecting from the orifice as a brown shrivelled scroll. ”

“ Breathing.—The inspiratory current passes inwards by the mouth opening in the larval lamprey, by the pituitary tube in Myxine, while in the adult lamprey both expiration and inspiration takes place through the external gill-openings. In the case of the lampreys the elastic skeleton of the branchial region (see below) plays an important part in respiration. The branchial region shows rhythmic contraction through the agency of the transverse muscles—and expansion, through the elasticity of the branchial skeleton—in the adult lamprey. ”

“ The basal portion, (a) by which the whole labial apparatus is attached to the head, Kirby regards as the mentum. The second division (d) he considers as more directly answering to what is strictly called the labium in other insects; and the terminal portion (e) is merely an additional articulation to it, divided into two, three, or more lobes. "At first you would imagine the terminal part of this organ to be the analogue of the tongue, or ligula F; as it is indeed generally regarded by modern Entomologists. ”

“ The lamprey, as I have already told you, ranks almost lowest among fishes, and consequently among vertebrate animals, of which fishes form the rear-guard. Indeed, it is almost stretching a point to consider her worthy to bear the proud title of a vertebrate at all; for the vertebral column, so clearly marked in other fishes, where it forms the large central bone, is only faintly indicated in certain species of lampreys, by a soft thread (or filament) , which is rather a membrane than a bony chaplet, and at the top of this mockery of a vertebral column is the creature's mouth. ”

“ The antennae are simple, consisting of from nine to thirty-one joints, which differ but little from one another; the number in each individual increases as the development progresses. The parts of the mouth are large, the ligula consists of one piece (Fig. 226, A) , but often has the appearance of being formed by two united pieces; on its extremity are seated two pairs of lobes.
Fig. 226.—Termes bellicosus. Labium, A, maxilla, B, of winged adult; lower face of each. (After Hagen.) ”

“ Lobulate: divided into, or with many small lobes or lobules.
Lobule: in Coccidae, one of the two distinct parts of which a lobe is sometimes composed.
Lobulus: the partly separated portion of the wings of some flies and of secondaries in some Hymenoptera: also used as = alula; q.v.
Lobus: of maxilla = galea; q.v.
Locomotion: organs of, are legs and wings.
Longicorn -ia: having the antennae as long or longer than the body; specifically the Cerambycid beetles. ”

“ The mouth itself is a large cavity communicating very freely with the exterior, but so completely shut off from the following parts of the alimentary canal that it is difficult to find the orifice of communication; the labium being much modified to form the posterior wall. For the capture of the prey, always living but of various kinds, a mechanism with great holding power and capable of rapid action is required. ”

“ Traill’s door in a state of complete insensibility, with froth at the mouth and a feeble pulse. An emetic, administered immediately, brought up a large quantity of laburnum seeds; after which the pulse became firmer, and sensibility quickly returned.—Mr. North has briefly noticed a similar case of a child, who after eating laburnum flowers, was seized with paleness and twitches of the face, coldness of the skin, laborious breathing, efforts to vomit, and great feebleness of the pulse. But recovery took place after the flowers were vomited. ”

“ It is very difficult to form an opinion as to the structure of the labium and other mouth-parts when the maxillae are not developed, as in these cases the parts are of a delicate membranous nature, and shrivel after death. ”

“ Food of Lampreys.—The lampreys feed on the blood and flesh of fishes. They attach themselves to the sides of the various species, rasp off the flesh with their teeth, sucking the blood till the fish weakens and dies. Preparations made by students of Professor Jacob Reighard in the University of Michigan show clearly that the lamprey stomach contains muscular tissue as well as the blood of fishes. ”

“ The prolongation (e) of the thin membrane (a) surrounding the anus (b) , that is, the rudiment of the abdomen, which sometimes carries caudal appendages, almost divides (in appearance, whether really I know not) the hindermost thoracic segment along the medio-dorsal line, into two parts. I have given the above drawing of these segments, but with the dorsal surface much flattened, in Coronula diadema; in most species of Balanus, however, the wedges formed by one segment being driven into another, are much sharper; on the other hand, in Xenobalanus they are nearly straight and transverse. ”

“ The labia majora resemble the skin of other portions of the body in that they contain papillæ, nerves, vessels, and Pacinian bodies. Internally they are lined with mucous membrane in which are numerous sebaceous follicles. A quantity of fat, areolar tissue, and tissue analogous to the dartos of the scrotum, including vessels, nerves, and glands, constitutes the contents of the labia, and gives them a rounded appearance, larger in front and decreasing in size toward the perineum. The extremities of these folds, joining together, form the anterior and posterior commissures of the vulva. ”

“ Thus when any extraneous material on the eye-ball, or the dryness of the external covering of it, or the coldness of the air, or the acrimony of some vapours, as of onions, stimulates the excretory duct of the lacrymal gland, it discharges its contents upon the ball; a quicker secretion takes place in the gland, and abundant tears succeed, to moisten, clean, and lubricate the eye. ”

“ In this case there exists a chain of associated actions, the secretion of the lacrymal gland is increased by whatever stimulates the surface of the eye, at the same time the increased abundance of tears stimulates the puncta lacrymalia into greater action; and the fluid thus absorbed stimulates the lacrymal sac, and its nasal duct in the nose into greater action. In a contrary direction of this chain of association the present increase of action is induced. First, the nasal duct of the lacrymal sac is excited into increased action by some pleasurable or painful idea, as described in Sect. ”