This species was first discovered by Pruner encysted in the livers of two negroes in Cairo. Bilharz reported two further cases in which the parasites were encysted in the liver and in the mucosa of the intestine; a few other observations have been made by Fenger, Aitken, Giard and Chalmas. Aitken’s report deals with soldiers of the British Colonies in Africa. The parasites were discovered in the liver as well as in the lung, and appear to have been the cause of death in one case (pneumonia, peritonitis).
Pruner has found the same parasite also in the liver of the giraffe.
It has recently been assumed that Porocephalus constrictus is the larva of Pentastoma moniliforme, Diesing, 1835, that attains a length of 70 mm. and lives in the lungs of African Pythonides. The larva is known to have been ejected from monkeys (Cercopithecus albogularis, Cynocephalus maimon), from the giraffe (Camelopardalis giraffa), from a species of hyæna (Proteles cristatus), and should be expected to occur frequently in smaller mammals which have been swallowed by African serpents of enormous size.
[The three species of Pentastomidæ, or tongue worms, found in man are Linguatula serrata, Frölich; Porocephalus armillatus, Wyman; and Pentastoma moniliformis, Diesing.
[(1) Linguatula serrata has been referred to under a great number of names.356 It is a frequent parasite in dogs, oxen and sheep; as an adult in the dog and also in the fox and wolf. The nymphal stage is found in rats, hares, rabbits, the horse, oxen, sheep, goats, pigs, camels, deer, the African and long-eared hedgehogs, porcupine, guinea-pig and peccary. In man it is found in both adult and nymphal stages. Sambon says the nymphal stage is of frequent occurrence, but is usually overlooked. Zenker, who first found it in man, obtained it in nine out of 160 post-mortems, usually encysted in the liver. It is then said to be harmless. Landon, in 1878, found the adult in man, the patient suffering from epistaxis for about seven years; in the end during a fit of sneezing the living parasite was ejected through the nostril. This case is of particular interest as it appears to suggest that this Acarid may now and then pass its entire development in the same host, or at any rate may actively migrate from the liver to the nasal cavities after a period of encystment in the liver or elsewhere, which has also been observed in herbivorous animals (vide also p. 526).
[It is recorded from man in Central America (Darling, Bull. Soc. Path. exot., 1912, v, p. 118; and again Arch. Int. Med., 1912, v, p. 401), also from Rio de Janeiro (Mem. Inst. Oswaldo Cruz, 1913, fasc. ii, p. 125) by Faria and Travassos.
[(2) Porocephalus armillatus, Wyman, is also known under a variety of names.357 This species is widely spread over tropical Africa. The adult stage is found in pythons and puff-adders, the nymphal in the chimpanzee, Sykes monkey, mandrill and other monkeys, the lion, leopard, banded ichneumon, Aard wolf, dog, black rat, South African reedbuck and the giraffe. The adult has never been found in man or any mammal. No fewer than sixteen cases of the nymphal form, Sambon tells us, have been found in man, and it is probably much more widespread than at present known. So far it has only been found in the African natives. This species has sixteen to seventeen body rings in the male, eighteen to twenty-two in the female, and the body does not taper as much as in the next species.
[(3) Pentastoma moniliformis, Diesing,358 is an Oriental species, found in India, Indo-China and South China, and the Malay Archipelago. The adult occurs in both the Indian and reticulated pythons. The nymphal stage has been found in monkeys, the tiger, the civet and the Indian otter.
[The nymph has twice been found in man; in one case in the liver of a Filipino, the other in the serous coat of the small intestine of a native of Sumatra.
[This species can be told by the female having twenty-nine to thirty-three body rings, the male twenty-six, and the annulations are more bead-like and less prominent than in the African species.
[In addition to these three, Sambon thinks it probable that others occur in man.—F. V. T.]
Other References to Pentastomidæ.
(1) “Die Wanderung des Pentastomum denticulatum beim Rinde,” Centralbl. f. Bakt. u. Parasitenk., Jan. 2, 1889, v (1), pp. 1–5, V. Bates.
(2) “Il Pentastoma moniliforme, Dies., nella pantera,” Med.-vet. Torino, 1877, 4 s., vi (12), pp. 529–532, R. Bassi.
(3) “On the Organization and Development of Linguatula (Pentastoma), accompanied with the description of a new species from the abdominal cavity of the mandrill,” Ann. and Mag. Nat. Hist., 1848, 2 s. ii (7), 2, pp. 69–70, v. Beneden.
(4) “De la Linguatula ferox (Pentastoma denticulatum aut serratum),” Bull. Acad. roy. d. Sci. d. Belg., 1855, xxii, pt. 1 (1), pp. 4–10, v. Beneden.
(5) “Note sur quelques pentastomes,” Bull. Acad. roy. d. Sci. de Belg., 1857, 26, 2 s., ii (5), pp. 29–30, v. Beneden.
(6) “Ueber das Pentastoma in de gekrösdrusen den Schafe,” Repert. d. Thierh. Stuttg., 1861, xxii, pp. 37–38, Collin.
(7) “Eine Linguatula aus der Mesenterialdrüse des Schafes und Dromedars als zweites ungesche. Stadium von Pent. taenioides,” Notiz. u. Tagsber. u. d. Geb. d. Nat. u. Heilk. Jena, 1862, v, pp. 127, 128, Colin.
Three separate regions can always be distinguished in the body of insects, namely, the head, thorax and abdomen. The HEAD is a roundish unsegmented capsule and possesses four pairs of appendages. The first pair are the various shaped feelers (antennæ), which are placed on the superior surface of the head next to the eyes; then more ventrally placed a pair of upper jaws (mandibles) without palpi and without articulations; they are powerful masticatory organs.359 The first pair of lower jaws (maxillæ) are jointed and bear a palpus (palpus maxillaris); the second pair of maxillæ are soldered together and form the lower lip (labium), and likewise carry a palpus labialis on each side. The upper lip (labrum), as well as the other parts (which, however, are only appendages), belong to the mouth, which is really formed of a number of closely united pieces. The mouth parts are modified according to the functions required of them. Coleoptera, Neuroptera, and Orthoptera have biting or masticatory mouth parts which conform with the scheme described above. In the licking mouth parts of the Hymenoptera the maxillæ and under lip are considerably elongated, while the mandibles retain their form and are used for triturating the food; in the Lepidoptera nearly all the mouth parts are shortened except the maxillæ, which form a long and sometimes spirally rolled suctorial proboscis; the Diptera and Rhynchota have piercing and sucking mouth parts. The mandibles and maxillæ are metamorphosed into needle-like structures, while the suctorial apparatus is formed by the labrum.
The thorax consists of three segments, which are frequently united; ventrally it carries three pairs of legs, which consist of a definite number of articulated pieces joined together. Their form also changes according to their function, so that legs for running, walking, digging, swimming, jumping, and preying are seen. A pair of wings are respectively attached to the last and last but one thoracic rings, and these may be traced back, not to metamorphosed appendages, but to tracheal branchia. They are composed of chitinous membranes supported by branched structures (veins or ribs). Their size and formation vary; they are seldom of equal size and form (Neuroptera); often the posterior wings are larger than the anterior wings, the former then only serving as protective coverings for the latter (Coleoptera), or the anterior wings are larger (Lepidoptera), or the posterior wings are shortened or are entirely absent (Diptera); and finally there are insects in which both pairs of wings are lacking.360
The abdomen retains its segmentation, but, with the exception of a few groups related to the primitive forms of insects, has no appendages in the imago condition; the abdomen usually consists of ten segments, on the last of which the anus is situated.
We need only observe the following characters in considering the anatomy of insects:—
The EPIDERMIS consists of the chitinous cuticle, which is separate from the cellular layer beneath (hypodermis); the various appendages are supported by the chitinous layer.
The INTESTINAL CANAL usually consists of the anterior, median and terminal intestine, and as a rule passes straight through the body; salivary glands discharge into the anterior part, and, in some cases, yield a stiffening secretion which serves for spinning webs; numerous or scanty hepatic tubes are appended to the median intestine, while on the border between the median and terminal intestine open four to six long tubes (vasa malpighiana), which act as urinary organs. Finally the end portion of the intestine carries various glands (anal and rectal glands, etc.).
The CENTRAL NERVOUS SYSTEM agrees in structure with that of the Annelids, but is more highly developed. The pharyngeal ring surrounds the front part of the intestine; the sensory nerves originate from its SUPERIOR PHARYNGEAL GANGLIA and are the seat of the higher psychical functions; the INFERIOR PHARYNGEAL GANGLIA govern the mouth parts, and in addition appear to regulate the movements (cerebellum) of the vertebrates.
The chain of GANGLIA lying on the ventral side of the abdomen consists primitively of pairs of ganglia corresponding with the twelve segments, which are connected by longitudinal and transverse commissures. But many changes in the ganglia may be seen in insects caused by partial or entire amalgamation of single ganglia, so that in a few cases only one abdominal ganglion is present. In conclusion, a definite INTESTINAL NERVOUS SYSTEM is always present.
Of the organs of sense the FACETTED EYES, situated at the sides of the head, deserve special mention, as do also the ORGANS OF TOUCH and SMELL, situated on the antennæ, and the ORGANS OF HEARING and taste, or finer sensations, situated at the mouth and in the buccal cavity.
The sounds emitted by insects are, as a rule, produced by the friction or beating of certain chitinous parts, but sounds are also produced in breathing (flies).
The ORGANS OF RESPIRATION, the so-called tracheæ, are highly developed; there are openings (stigmata) at the sides of the body which draw in air by means of the active participation of the muscles of the body. The number of stigmata varies between two and ten pairs; the tracheæ themselves branch off from the trunks in the most varied manner, and carry air to the internal organs.
The colourless BLOOD circulates between the tissues and organs, and is kept circulating by the contraction of a chambered dorsal vessel provided with ostia, and which terminates in a short aorta opening at the anterior end.
Insects are SEXUALLY DISTINCT; their sexual glands are in pairs and have a tubular structure, but the testicular tubules are united together by a capsule into an oval testicle; exceptionally, also, the excretory canals are double, as also the sexual orifices; usually the paired canals unite into a single oviduct or spermatic duct which terminates at the posterior end of the body after receiving the products of various glands.
As to the HISTORY OF THE DEVELOPMENT of insects, all that is necessary to mention here is that the young hatched from eggs only exceptionally (as in Apterygota) resemble the adult parent (insecta ametabola); as a rule they differ from them not only in the shape of the body, but also more or less by their manner of life, and only attain the form of the parent through METAMORPHOSIS. This is a gradual process (insecta hemimetabola) in the Rhynchota and Orthoptera, or a sudden one with a stage of inanition (insecta metabola) in the other orders. This stage of rest or inanition, the PUPA, concludes the larval life (caterpillar, maggot, etc.); during the pupal stage no nourishment at all is taken, but the internal organs undergo changes; in some forms the rest is not absolute, as voluntary local movements may take place (pupæ of gnats).
The insects are divided into numerous orders according to the form of the mouth parts, the structure of the wings, as well as the manner of the development; with the exception of the lowest group (Apterygota), which is most nearly related to the ancestors of the insects, and which has no wings and undergoes no metamorphosis, all the remaining orders, which are termed Pterygota, have wings on the thorax, though there are, of course, a few species and families of this group which have lost their wings.
The Pterygota include—
(1) Orthoptera.—Biting mouth parts, anterior wings leathery, posterior wings thin, folded longitudinally; metamorphosis incomplete (grasshoppers, crickets, cockroaches).
(2) Pseudoneuroptera.—Biting mouth parts, wings of equal size, thin, not folded up (dragon-flies, hair and feather lice, termites).
(3) Rhynchota or Hemiptera.—Mouth parts formed for puncturing and sucking; wings alike, or the anterior wings may be thickened, parchment-like at their base (plant lice, cicadæ, bugs and true lice).
(4) Neuroptera.—Biting mouth parts; wings alike, thin; metamorphosis complete (ant-lions, lace-wing flies, etc.).
(5) Trichoptera.—Licking mouth parts; anterior wings narrow, posterior wings longitudinally folded, both ornamented with little hairs; the larvæ are worm-like in form, live in water, and breathe through tracheal gills (may flies, etc.).
(6) Lepidoptera.—Suctorial mouth parts; wings covered with scales (butterflies).
(7) Coleoptera.—Biting mouth parts; anterior wings thickened and differ in colour, appearance and function from the thin, folded posterior wings (beetles).
(8) Hymenoptera.—Mouth parts for licking and biting; the wings alike, membranous (ichneumon flies, ants, wasps, bees, humble bees).
(9) Diptera.—Mouth parts formed for puncturing, sucking or licking; posterior wings degenerated (gnats, flies, gadflies, fleas).
(10) Strepsiptera.—Anterior wings shortened; the female without wings and living parasitically (fan-wings).
The parasites of man occur amongst the Rhynchota, Coleoptera, and amongst the Diptera.
[The most usual and recent classification of the Hexapoda is the following:—
(1) Aptera.—Wingless insects; scarcely any metamorphosis.
(2) Neuroptera.—Four membranous wings, frequently with much network; the front pair not much, if at all, harder than the under pair; the latter with but little or no fan-like action in closing; mandibulate; metamorphosis variable, but rarely complete.
(3) Orthoptera.—Four wings; front pair coriaceous or leather-like, usually smaller than the other pair, which are of more delicate texture and contract in repose like a fan; mandibulate; metamorphosis complete.
(4) Thysanoptera.—Four very narrow fringed wings; mouth imperfectly suctorial; metamorphosis slight.
(5) Hemiptera.—Four wings; the front pair either all transparent or with the basal half leathery; mouth suctorial; metamorphosis slight.
(6) Diptera.—Two membranous wings only; mouth suctorial, very varied; metamorphosis complete.
(7) Lepidoptera.—Four large wings covered with scales; mouth suctorial, metamorphosis great.
(8) Hymenoptera.—Four membranous wings; front pair larger than hind, which do not fold up in repose; mandibulate, sometimes with a tubular proboscis; metamorphosis complete.
(9) Coleoptera.—Four wings, the front pair hard and horny (elytra), meeting in a line over the back and covering the delicate hind pair; mandibulate; metamorphosis complete.
[There are two other well-known arrangements, namely, Packard’s and Brauer’s, of recent date, but the one given here, which is based on Linnaeus’ grouping by Dr. Sharp, is by far the simplest.—F. V. T.]
Order. Rhyncota.361
The lower lip forms a long thin tube that can be turned back (rostrum), and within which lie the setaceous mandibles and maxillæ; the first thoracic segment is not united with the two posterior ones; the anterior wings are usually leathery as far as the centre.
(a) Rhyncota aptera parasitica.
Family. Pediculidæ (Lice).
The lower lip is transformed into a projecting rostrum provided with barbed hooklets in which the hollow extensile sucker (maxillæ and mandibles) is situated; no wings; no metamorphosis; only simple eyes; the antennæ are five-jointed, the feet possess hook-like terminal structures; the barrel-shaped eggs (nits) are deposited on the hair of the host.
[The lice or Pediculidæ are also known as Anoplura and Siphunculata.
[They have been split up into a number of families and sub-families and a number of genera, but as far as this work is concerned it is best to retain the single family Pediculidæ.
[Only the three species mentioned here are common parasites of man, but now and then horse and cattle and sheep lice, Hæmatopinus, may cause transitory annoyance.—F. V. T.]