The body is elongated, gradually decreasing in thickness towards the back. The rostrum is almost spherical, and is beset with five or six rows of recurved hooks. The males measure 10 to 15 cm. in length, the females 30 to 50 cm.; the eggs are provided with three shells, of which the middle one is the thickest. The eggs measure 0·08 to 0.1 mm. in length. The giant Echinorhynchus occurs especially in the intestinal canal of the domestic pig; it is less common in other mammals. It bores deep into the mucous membrane with its rostrum, and causes an annular proliferation around the perforated spot; occasionally also it causes perforation of the intestine.
It is doubtful whether the giant Echinorhynchus occurs in man. Leuckart admitted that there were a few positive cases. According to Lindemann, Ech. gigas occurs in human beings in South Russia, and its presence is not rare. This statement, however, has not been confirmed. Its presence in man is by no means impossible, as its intermediary host, the cankerworm, or cock-chafer (Melolontha), is, according to Schneider, occasionally eaten raw by human beings. According to Kaiser, the golden beetle (Cetonia aurata) and, according to Stiles, another beetle in America (Lachnosterna arcuata) are also intermediary hosts.
Echinorhynchus hominis, Lambl, 1859.
This term is applied to an Echinorhynchus found by Lambl in the intestine of a boy who had died of leucæmia; the worm was 5·6 mm. in length, and the almost spherical head was beset with twelve transverse rows of hooks.
Echinorhynchus moniliformis, Bremser, 1819.
The male is 4 cm. in length, the female 8 cm. long. This species lives in the intestine of field-mice, rats, marmots and Myoxus quercinius. A beetle (Blaps mucronata) is the intermediary host.
This species has also once been artificially cultivated in man (Grassi and Calandruccio).
Very long thin worms similar to Filariæ, which, in their adult condition, live free in brooks, pools and springs; the mouth and the commencement of the intestine are obliterated; there are no lateral ridges, and the muscular system presents a structure different to that of the Nematoda. The posterior end of the male is split, and spicules are lacking; there are two testicles. In both sexes the genitalia discharge through the terminal gut.
The larvæ, which carry a rostrum beset with hooks, force themselves into the larvæ of water-insects; more rarely they invade molluscs, and they then become encysted within the body of the host. According to Villot, at least a part of them attain the intestine of fishes, where they again become encysted, and after a period of rest they travel into the tissues of their hosts, and finally again reach the exterior by way of the intestine, where they then become adult. In most cases, however, the gordius larvæ are taken up by predacious water insects; they live for a while in the body cavity of these insects, undergo a metamorphosis, and finally wander into the water.
A few species invade man accidentally with water, in which case they are usually vomited up:—
Gordius aquaticus, Dujardin, 30 to 90 cm. in length (Aldrovandi, Degland, Siebold, Patruban).
Gordius tolosanus, Duj., 11 to 13 cm. in length (Fiori).
Gordius varius, Leidy, 10 to 16 cm., female, up to 30 cm. in length (Diesing).
Gordius chilensis, Blanch. (Guy). Gordius villoti, Rosa (Bercutti, Camerano); Gordius tricuspidatus, L. Def. (R. Blanchard), Gordius violaceus, Baird (Topsent), and Gordius pustulosus, Baird (Parona).
Fig. 348d.—The internal organs of the leech. The creature has been opened from the dorsal surface, and part of the intestine has been removed. The testicles, with vas deferens, may be seen between the blind ducts of the intestine; beyond these on either side the segmental organs. The female genital organs are in front of the most anterior pair of testicles. (After Kennel.)
The Hirudinea, which have been appropriately included amongst the Annelida, differ in many respects from the typical members of the group; their body is long and flat, it lacks the parapodia that are characteristic to all forms of Annelida; but, on the other hand, possesses a terminal posterior sucker, and in many species there is also an anterior sucker. The mouth is terminal at the anterior end, the anus lies dorsally above the posterior sucker (fig. 348D). The body is segmented, but this is less manifest in the body covering than it is in the arrangement of the internal organs; the segmentation, nevertheless, is also indicated exteriorly by the appearance of the cutaneous sensory organs which correspond to the segments. This shows what the condition of the ganglia in the abdominal ganglion chain has taught us, that the anterior and the most posterior segments are considerably abbreviated—a part of the latter taking part in the formation of the suctorial organs. In a great many species the skin is distinctly annulated, four or five of such rings, at least in the central region of the body, appearing on one segment of the body. The condition of their body cavity is another peculiarity of the Hirudinea; it is narrowed by the powerful development of the connective tissue and the muscular system into four tubular sinuses, which have the appearance of blood-vessels. There are usually one dorsal and one ventral median trunks, as well as two lateral trunks; in addition, a particular blood-vessel system exists.
The skin consists of a very thin cuticle that is cast off from time to time; it is secreted by the underlying cylindrical epithelium, which contains numerous goblet cells. The muscular system is strongly developed; it consists of long tubular fibres, which run circularly, longitudinally and in the dorso-ventral direction; the muscular system is subject to a particular expansion in the clinging organs and at the commencement of the intestine. On the whole, the alimentary canal represents a tube running straight from the mouth to the anus, which possesses a number of blind sac-like protuberances at the sides varying according to the species. The most anterior section, the pharynx, in the leeches with maxillæ carries three chitinous, semicircular plates furnished with teeth—the jaws—which serve to tear up the epidermis in order to open the blood-vessels; in the leeches with rostra a long protractile proboscis rises from the base of the elongated pharynx. Numerous salivary glands, the secretion from which possesses toxic properties, discharge into the pharynx. The œsophagus, which follows the pharynx, and to the exterior of which numerous radiary muscles are fixed, is a suctorial organ in its entire structure. The nutriment in the larger species consists of the blood of vertebrate animals, in smaller species and in the young stages the food consists of small invertebrate animals.
The NERVOUS SYSTEM exhibits the typical structure of other segmented worms; the sensory organs consist of the previously mentioned goblet-shaped cutaneous sensory organs, of the organs of taste, and of eyes, the latter frequently being present in large numbers.
The EXCRETORY or segmental organs exhibit many peculiarities, which cannot, however, be detailed here. They commence with funnels in the lacunes of the body cavity, and usually discharge on the ventral surface.
Almost all the Hirudinea are hermaphrodite and copulate reciprocally. The two ovaries are very small, and the oviducts that proceed from them soon unite into a common duct, which then passes into the uterus and discharges through the short vagina in the median line of the ventral surface behind the male organs into the so-called clitellar region. The male sexual apparatus consists of symmetrically arranged testicles, varying in number according to the species, the short vasa efferentia of which, one by one, run into the vas deferens, passing towards the front on each side. In front, at about the level, or a little in front, of the female genitalia, the two vessels pass into a convoluted mass of tubes to the so-called epididymis, and then discharge into the single protractile penis (fig. 348D).
All leeches deposit so-called COCOONS. These are small barrel-shaped or pouch-like bodies, which are surrounded by a thicker shell and contain a number of eggs in a large mass of albumen; the albumen originates from glands of the generative organs, the shell substance from cutaneous glands of the clitellar region.
Family. Gnathobdellidæ (Leeches with Jaws).
These are distinguished by the possession of usually three jaws in the pharynx; the body consists of twenty-six segments. The posterior sucker is large and flat; the anterior sucker is smaller. The Hirudinea have five pairs of eyes, the Nephelinæ have four pairs.
Genus. Hirudo, L., 1758.
The entire body consists of 102 annulations, five appearing on one segment in the central region of the body. The pharynx has three semicircular jaws, the arched border of which is beset with numerous teeth (50 to 100). The male sexual orifice lies between the thirtieth and thirty-first rings, the female orifice between the thirty-fifth and thirty-sixth. There are numerous species, some of which are utilized for medicinal purposes.
Fig. 348e.—Hirudo medicinalis. a, anterior end, with open buccal cavity, with the jaws, J, at the; b, one jaw isolated. (After Claus.)
Hirudo medicinalis, L., 1758.
It occurs in numerous colour varieties, one of which has been designated Hirudo officinalis, Moq.-Tandon. Usually the dorsal surface is greyish-green and is marked with six rusty-red longitudinal stripes. The ventral surface is olive-green, more or less spotted with black, and marked at the sides with a black longitudinal line. The length averages 8 to 12 to 20 cm. This leech lives in swamps, ponds and brooks, overgrown with plants and having a muddy bed. The cocoons are deposited in the soil at the sides. Europe, as well as North Africa, is its home. At the present day it has been exterminated from most parts of Central Europe, but it is still very common in Hungary. Its use for medicinal purposes is well known. A large leech can suck about 15 grs. of blood, and about the same amount is lost through secondary hæmorrhage.
Hirudo troctina, Johnston, 1816.
Syn.: Hirudo interrupta, Moq.-Tandon, 1826.
This species measures 8 to 10 cm. in length. The back is greenish, with six rows of black spots surrounded by red; the lateral borders are orange-coloured; the abdomen spotted or unspotted. Its habitat is in North Africa and Sardinia. It is applied medicinally in England, Spain, France, Algeria, etc.
Genus. Limnatis, Moq.-Tandon, 1826.
Nearly related to Hirudo, but is differentiated by a longitudinal groove on the inner surface of the upper lip of the anterior sucker. The jaws are furnished with over 100 very sharp toothlets.
Limnatis nilotica, Savigny, 1820.
Syn.: Bdella nilotica, Sav.; L. nilotica, Moq.-Tandon; Hæmopis (vorax), Moq.-Tandon, 1826, p. p.; Hæmopis sanguisuga, Moq.-Tandon, 1846 (nec Hir. sanguis, Bergm., 1757).
This species measures 8 to 10 cm. in length, and becomes gradually more pointed towards the front; the body is always soft. The back is brown or greenish, and has usually six longitudinal rows (rarely only two or four) of black dots. The abdomen is dark; but numerous colour variations occur.
The native place is North Africa, especially the coastal regions; it is also found in the Canaries, the Azores, Syria, Armenia, Turkestan, perhaps also Southern Europe. It is taken into the mouth with drinking water, and may settle in the pharynx, larynx, œsophagus, and nasal cavities of human beings. This species has also been observed in the vagina and on the conjunctiva. It is equally fond of attacking domestic animals.
Hirudo mysomelas (Senegambia) and Hirudo granulosa (India) are placed with this genus, and, like our leech, are also used for medicinal purposes.
Genus. Hæmadipsa, Tennent, 1861.
These leeches live on land, and measure 2 to 3 cm. in length. About a dozen species are known. They are a veritable scourge to persons in the tropics (Asia, South America), as they attack them to suck their blood. They are able to force their way even under close-fitting garments, so that it is difficult to protect oneself from their assaults (Hæmadipsa ceylonica, Bl., and other species).
Family. Rhynchobdellidæ (Leeches with Rostrum).
These are furnished with a proboscis in lieu of the jaws; the segment consists of three annulations.
Genus. Hæmentaria, de Filippi, 1849.
Hæmentaria officinalis, de Fil.
Inhabit Mexico, where they are used for medicinal purposes.
Genus. Placobdella, R. Blanch.
Placobdella catenigera, Moq.-Tandon.
Indigenous to South Russia, Hungary, Italy and South France. It is a parasite of the swamp turtle, but frequently attacks human beings.
Bilaterally symmetrical segmented animals which are covered with a thick cuticle that is frequently calcareous (Crustacea), but always thinner between the segments; they carry (primitively) a pair of jointed appendages on every segment.321 The segments of the body are uniform in certain regions, but differ from those of contiguous regions, so that it is easy to distinguish three parts (head, thorax and abdomen), each composed of segments. The cephalic segments are always formed into a uniform head, the segmentation being scarcely recognizable at either end; the thoracic segments may also fuse, or part or all of them may coalesce with the head; the abdomen, as a rule, retains its segmentation, but this may possibly also be lost, in which case it is [sometimes] united to the cephalothorax. The structure of the three regions depends mostly on the varying form and function of the appendages: those on the head are primitively locomotive organs (and frequently are still so in the early stages), but they become transformed into feelers and mouth-parts (mandibles, maxillæ); the limbs of the thorax, however, usually retain their ambulatory functions, as frequently do those of the abdomen; sometimes, however, the abdominal limbs disappear, entirely or partly; in the latter case they are then utilized for other purposes.
In their organization the Arthropoda approach the segmented worms.
The Arthropoda are generally divided into five groups (Crustacea,322 Protracheata, Arachnoidea, Myriapoda,323 and Insecta or Hexapoda), of which only the Arachnoidea and the Hexapoda interest us here.
The head and thorax are always united together; the abdomen is either segmented or without exterior segmentation, in which case it is united with the cephalothorax.324 The number of pairs of appendages amount to six, of which the two front pairs, the cheliceræ and the pedipalpi, are attached to the head region and the four remaining pairs to the thoracic region.325 The abdomen in the adult condition has no appendages. The Arachnoids are air-breathers, and for this purpose are either provided with tracheæ or with so-called lung-sacs, or they breathe through the surface of the body. Some aquatic forms breathe by gills.
There are eight or ten orders of Arachnoids,326 of which, however, only two, the Acarina and the Linguatulida, have to be considered here.327
Order. Acarina (Mites).
Small Arachnoids, the three parts of the body of which are, as a rule, coalesced; it is only rarely that a faint line indicates the division between a cephalothorax and abdomen. The two appendages on the head are designed for biting or puncturing and sucking, and vary according to their use. The cheliceræ328 are fang-like jaws or puncturing bristles forming a kind of rostrum, the pedipalpi are claw-like or shear-shaped, or form a suctorial proboscis.329 The four pairs of legs are usually well developed, more rarely they are rudimentary or have partly vanished; many parasitic forms are provided with pedunculated suckers [ambulacra—F. V. T.]. Respiratory organs (tracheal tufts) may be present or absent. The nervous system is reduced to a minimum, eyes are usually lacking. The intestine, situated in the central part, generally has three blind appendages; the anus is situated on the venter above the posterior end. Sexes separated; nearly all the species deposit eggs, from which six-legged larvæ hatch. The Acarina live either free in the water or in moist soil, or they are parasitic on plants and animals.330
Family. Trombidiidæ (Running Mites).
Soft-skinned Acarina with tracheæ and with two eyes, usually pedunculated; they are often brightly coloured; cheliceræ lancet- or claw-shaped; pedipalpi claw-like; legs composed of six segments, with suctorial discs between the terminal ungues.331 Larvæ six-legged. To the latter belong the larvæ of several species of Trombidium such as:—
Genus. Trombidium, Latreille (and Leptus).
Leptus autumnalis, Shaw, 1790.
Leptus occur as parasites in the human skin and cause a cutaneous disease known as autumn erythema, and produce a very unpleasant sensation on account of the troublesome itching; in children it is very often accompanied by fever.332
Formerly these mites were considered adult forms, but when they were recognized as mite larvæ they were taken for those of the spider-mite (Tetranychus telarius); the investigations of Hanstein, however, showed this to be a mistake. When Henking first investigated the development of Trombidium fuliginosum, parasitic in the larval stage on vine-fretters, he demonstrated the occurrence of a form very similar to Leptus autumnalis, and the “autumn, grass, or gooseberry” louse was commonly designated the Trombidium larva. Even before Henking’s work it had been described by Mégnin as the larva of Trombidium holosericeum, a red-coloured species, frequently occurring in spring and summer on the ground, trees, etc. This assumption, however, as Moniez was the first to explain, is not correct; indeed, as many as three species come under consideration: T. gymnopterosum, L., T. fuliginosum, Herm. (according to Brucker), and two species known hitherto only in the early stage, T. striaticeps, Helm. et Oudem., and T. poriceps, Helm. et Oudem., which are not only parasitic on mammals, but on birds, on Arthropods and especially on insects. Arthropods appear to be the normal hosts for the larvæ.
Fig. 350.—Leptus autumnalis: the so-called proboscis is formed around the hypopharynx sunk into the skin. 100/1. (After Trouessart.)
The above-mentioned forms invade the skin of man by means of their oral apparatus, by preference invading the orifices of the sebaceous glands so as to suck the blood; around the point attacked there arises a wheal about the size of a lentil, and around the inserted hypopharynx a fibrinous secretion, the “proboscis,” which, however, is a product of the host, just as chitinous secretions are provoked by Trombidia parasitic on Arthropods.
Further species, analogous in habit to Leptus autumnalis, are described by Riley from Central and South America as L. americanus and L. irritans.
[L. autumnalis attacks small mammals by preference, such as moles and hares, which are often literally covered with them. Dogs are also subject to their attack, and cats suffer similarly. This mite also frequently appears in colonies on cows; cavalry horses after autumn manœuvres often suffer from an erythematous affection about the hocks and knees due to this pest.
[A number of Leptus, so far undescribed, occur abroad which attack man in the same way as L. autumnalis in Europe. Dr. Durham has brought me specimens from British Guiana called bête rouge; this species works under the skin much as does our European species, but it is very distinct, being considerably larger.—F. V. T.]
Trombidium tlalsahuate, Lemaire, 1867.
T. tlalsahuate occurs in Mexico under conditions similar to those of Leptus here. It also frequently attacks men, and especially fastens itself on to the eyelids, in the axillae, navel, or on the prepuce; it induces itching and swelling of the parts affected, and sometimes even causes suppuration; the symptoms, however, generally disappear after a week and remain localized.333
Other species of mites which attack man are reported, mostly by travellers, from various other places; zoologically, however, there is little known about them. The pou d’agouti in Guiana, niaibi in New Granada, colorada in Cuba, mouqui in Para, and the buschmucker in New Guinea represent a few of these.
Akamushi or Kedani.
In a few districts of Japan there occurs a serious illness, with a mortality of 40 to 70 per cent. It is called river or flood fever, and the Japanese doctors have connected it with a small mite (akamushi, kedani). Baelz has opposed this opinion on the grounds that he has repeatedly observed the same species of mite in his dwelling without any subsequent illness occurring. According to Keïsuke Tanaka, however, a connection certainly does exist, inasmuch as the akamushi, like Leptus, attacks persons to suck blood. If the mite is not removed, or if the spot attacked is injured by scratching, etc., a papule surrounded by a red area forms, and a pustule ensues; and finally a black scab covers the seat of injury. The lesion becomes the point of entrance of bacteria, especially a species of proteus which produces river fever. If the mites are carefully removed no general illness takes place.
The orange-red mites, which we only know in their larval condition, measure 0·16 to 0·38 mm. in length by 0·10 to 0·24 mm. in breadth. They have leg-like palpi with three joints, hirsute bodies, and very hairy legs composed of five segments, terminating with three ungues.
Family. Tetranychidæ (Spinning Mites).
These have tracheæ and eyes; the palpi are composed of four segments, of which the last but one has a powerful claw. The legs have six segments with sucker discs between the claws.
[The red spiders or spinning mites (Tetranychi) are usually placed in the family Trombidiidæ.—F. V. T.]
Genus. Tetranychus, Dufour.
Tetranychus molestissimus, Weyenbergh, 1886.334
Found in Argentine and Uruguay on the under surface of the leaves of Xanthium macrocarpum; it attacks mammals and men, producing severe itching, accompanied by fever in the latter.
It has been asserted by Haller that the Cape ailment (Port Natal sickness) is caused by mites, but this statement has been contested.
Tetranychus telarius, L., 1758,335 var. russeolus, Koch.
This common spinning mite likewise attacks human beings, but the papules produced by it very soon disappear.
Family. Tarsonemidæ.
A family distinguished by complete sexual dimorphism, the species of which are provided with tracheæ; the legs have five segments; the terminal segments of the front pair of legs of both sexes possess a claw; the terminal segment of the posterior pair of legs of the male likewise has a claw. In the female this pair of legs, like the second and third pairs of both sexes, is provided with two hooklets and a sucking disc. The cuticle of the body on the back is “annulated.”
[This family of small transparent mites live normally as plant parasites. The last two pairs of legs are widely separated from the two front pairs.—F. V. T.]
Genus. Pediculoides.
Pediculoides ventricosus, Newport, 1850.
Syn.: Heteropus ventricosus, Newport, 1850; Acarus tritici, Lagrèze-Fossot, 1851; Physogaster larvarum, Lichtenstein, 1868; Sphærogyna ventricosa, Laboulbène and Mégnin, 1885.
Males are oval in shape, 0·12 mm. in length and 0·08 mm. in breadth, flattened. There are six pairs of chitinous hairs on the dorsal surface and a lyre-shaped lamella on the posterior part. The female in the non-gravid state is cylindrical in form, 0·2 mm. in length and 0·07 mm. in breadth; when gravid the posterior part of the body becomes enlarged into a ball, which may attain 1·5 mm. in size, as in the case of Pulex penetrans and of the female Termites. On emerging the young are already provided with four pairs of legs and copulate soon after birth.
Fig. 353.—Pediculoides ventricosus. a, male; b, young female; c, gravid female. Enlarged. (After Laboulbène and Mégnin.)
These animals live on the stalks of cereals, and feed on vegetable and animal juices; they are also found on corn-infesting insects. They invade the barns and seek out the insects living in the dry grains of corn, or wait for an opportunity of obtaining food. They have been repeatedly observed on human beings, particularly labourers occupied in handling grain; their bite causes severe irritation, local elevation and reddening of the epidermis, as well as fever. It cannot be positively asserted that all cases of the occurrence of cereal mites on man relate to P. ventricosus, as the descriptions are often insufficient. Geber states that one form is Chrithoptes monunguiculosus, or Acarus hordei; Flemming mentions Tarsonemus uncinatus; Koller Oribates sp.; and Karpelles Tarsonemus intectus.
[The pregnant female Pediculoides has a large round inflated abdomen, in which the ova hatch and the young mature. Later they escape from the parent as adults.—F. V. T.]
Genus. Nephrophages.
Nephrophages sanguinarius, Miyake and Scriba, 1893.
Males measure 0·117 mm. in length and 0·079 mm. in breadth; females up to 0·360 mm. in length by 0·120 mm. in breadth. The head is provided with two very large scissors-like jaws and two large round eyes. The legs are composed of five segments and are all of equal length; the three anterior pairs of legs have pedunculated ambulacra, the posterior ones terminate in a claw. The cuticle on the back is thickened in three places, shield-like; the abdominal surface without scutellum is longitudinally striped and is beset with chitinous hairs. Colour greenish to brownish-yellow. Eggs 0·046 to 0·040 mm.
The authors discovered these mites, but always dead, in the urine of a Japanese suffering from fibrinuria complicated with chyluria and hæmaturia. They surmised that they were endoparasites, probably situated in the kidney; but this view is not convincing, though they also report that for a week, day after day, the mites were found in the patient’s urine, as well as in urine drawn off by means of a catheter, and in the water used to wash out the bladder (one or two specimens and an egg). The statement that these mites have large eyes makes the discovery suspicious, to say the least. The significance of the discovery is not supported by the further statement that Disse is supposed to have found an encapsuled mite closely related to the Tyroglyphides on the wall of the vena cava.
In the case of Marpmann, who found a dead Acarid in the urine of a man suffering from chronic nephritis, and in whom later examinations proved negative, the author himself was of opinion that the mite had reached the urine from outside.
We are certainly acquainted with mites living endoparasitically, namely, the Cysticolæ, Analgesinæ, of which Laminosioptes gallinarum live in the intramuscular and subcutaneous connective tissue of fowls, and Cytoleichus sarcoptoïdes in their air sacs. Another kind of mite (Halarachne halichœri) is occasionally found in the nasal mucous membrane of the seal (Halichœrus grypus), and, quite recently, Pneumonyssus simicola, which is more nearly related to Halarachne, has been found in the lung of Cynocephalus sp. It is therefore not improbable that endoparasitic mites are found in man; but no definite discovery has yet been made.
Family. Eupodidæ.
Small tracheate mites, with moderately long or short pedipalpi, composed of four segments, of which the last segments bend; cheliceræ forceps-shaped, with serrated edges; legs with two claws, more rarely with one, and terminating in a tuft ornamented with fine hairs; genital orifices on the abdomen, surrounded by a circle of little hairs. Most species live free—one lives parasitically on the bodies of slugs.
Genus. Tydeus, Koch.
Tydeus molestus, Moniez, 1889.
Male, 0·2 mm. in length, 0·125 mm. in breadth. Females, 0·225 mm. in length, 0·135 mm. in breadth; gravid female 0·315 to 0·360 mm. in length and 0·180 mm. in breadth. They were observed by Moniez on an estate in Belgium, whither the creature had apparently been imported twenty-five years previously with Peruvian guano; they appeared regularly in the summer and remained until the first frost set in; they were found on grass-plots, on trees and bushes in masses; they regularly attacked human beings, mammals and birds, tormenting their hosts in a terrible manner.
Family. Gamasidæ (Coleopterous or Insect Mites).
Cheliceræ chelate or styliform; pedipalpi filiform; the legs are composed of six segments with two terminal ungues and a bladder-like sucking disc [caruncle—F. V. T.]. Stigmata situated between the third and fourth pairs of legs; the cuticle thickened, leather-like; no eyes; the larvæ have six legs.
The Gamasidæ are predaceous on small insects and other mites; some are parasitic on insects, and one is noticeable as a pest on birds, etc.
Genus. Dermanyssus, Dugés.
Dermanyssus gallinæ, de Geer, 1778.
Syn.: Pulex gallinæ, Redi, 1674; Atarus gallinæ, de Geer, 1778; Dermanyssus avium, Dugés, 1834.
The male measures 0·6 mm. in length by 0·32 mm. in breadth; the female 0·7 to 0·75 mm. in length by 0·4 mm. in breadth. The body is somewhat pear-shaped; the colour whitish, reddish, or reddish-black, according to the contents of the intestine. The legs are fairly short and strong. During the day they live concealed in the nests, cracks, etc., of the hen-house, and at night attack the inmates in order to suck their blood; they rarely remain long on the birds. They have been repeatedly found on persons, on whose skin they produce an itching eruption.
Dermanyssus hirundinis, Hermann, 1804.
Syn.: Acarus hirundinis, Herm., 1804.
Of a brownish colour, 1·2 or 1·4 mm. in length; lives in the nests of swallows and is occasionally found on man.
[The red hen mite (Dermanyssus gallinæ) not only attacks poultry and man, as stated above, but is found on all birds and many mammals. The D. gallinæ is the same as D. avium. The species found in swallows’ nests is also said to be the same. This mite can remain for weeks without any food from its normal host. They only attack man when entering or cleaning dirty and neglected fowl-houses; they do not produce a true dermatosis. They chiefly attack the backs of the hands and forearms of those who constantly attend poultry and give rise to symptoms similar to the papular eczema of scabies. That they may remain some time upon the human body we know from the following cases out of many recorded: Geber observed that the Dermanyssus had caused a diffused eczema on a woman, which lasted four weeks and then disappeared. The tique of F. V. Raspail is the bird Dermanyssus; he records children and adults being attacked not only when handling pigeons, but even when walking in a garden manured with pigeons’ dung. The affection soon disappeared when the pigeons were destroyed and the excreta buried. I have frequently heard of poultrymen being seriously attacked by this pest.—F. V. T.]
Genus. Holothyrus.
Holothyrus coccinella, Gervais, 1842.
Measures 5 mm. in size; lives on birds in the Island of Mauritius; ducks and geese frequently fall victims to its bite; it also attacks human beings, on whose skin it causes severe burning and swelling, but no reddening; it may be dangerous to children, especially by settling in the oral cavity.
Other Gamasides occasionally occur in man, for instance, according to Moniez, Leignathus sylviarum, Canestr. et Fanzago; according to Neumann Lælaps stabularis. The former live normally in the nests of various species of Sylvia, Lælaps on dried vegetable substances, also in houses.
[Marchoux and Conoy (Bull. Soc. Path. exot., 1912, v, No. 10, pp. 796–798) found Leishman granules in Lælaps echidninus. It is assumed that Leishman granules may be found in most Arachnoids, and have no connection with Spirochæta.—F. V. T.]
Family. Ixodidæ (Ticks).
Comparatively large Acarines with a leathery skin; they are flattened in form, but after sucking blood the abdomen becomes spherical; the cheliceræ are rod-like and possess a serrated terminal joint, bent hook-like; the median parts of the pedipalpi (maxillæ) form a rostrum furnished with barbed hooks (fig. 359); the maxillary palpi themselves are club-like or rounded; the legs are composed of six segments with two terminal ungues, often also with “sucking discs”; the stigmata are at the sides of the body, posterior to the fourth or third pair of legs. The larvæ are six-legged.
[The true ticks (Ixodidæ) are all blood-suckers, and as far as is known they do not take vegetable food at all. Not only are the Ixodidæ important as actual parasites, but they are most so on account of the fact that they are the active agents in carrying various diseases in animals and apparently in man. It has been conclusively proved that the bont tick (Amblyomma hebræum) is the carrier of the fatal “heart-water fever” so rife amongst sheep in South Africa, that the dog tick (Hæmaphysalis leachi) is the agent by which the protozoa that cause malignant jaundice in dogs are distributed, that Texas fever in cattle is spread by Rhipicephalus annulatus, and Coast or Rhodesian fever by R. appendiculatus and R. simus. Their importance as disease carriers amongst mammals is therefore considerable, and it may prove to be so for man.336 They frequently attack man, but chiefly, according to my observations, in their early stages in Europe; this is not so, however, abroad. The life-history of a number of ticks has been clearly demonstrated. Mr. Wheler has shown that in Ixodes reduvius it is as follows: the female deposits her eggs in masses upon the ground, gradually reducing in size as the eggs pass out, until she finally remains a mere shrivelled empty bag and then dies. The eggs are oval, golden brown in colour and smooth; in length they are 0·59 mm.; as in all Ixodidæ they are covered with a glutinous secretion, by means of which they adhere together in masses. These egg masses may be deposited anywhere on the ground, but amongst rough, coarse herbage seems to be the favourite place. The egg stage may last as long as twenty-two weeks, or it may only take eight weeks. In the case of the bont tick a single female may deposit 15,000 or more eggs. The process of egg-laying is described as follows by Mr. Wheler: “When egg-laying is about to take place, the head is further depressed till it rests close against the under side of the body. In this attitude the end of the rostrum actually touches the genital orifice, the palpi being at the same time widely opened out. Behind the head and from beneath the shield, at what for the purposes of explanation may be described as the back of the neck, a white, perfectly transparent, delicate gelatinous membrane is brought down through inflation, either with air or with a transparent fluid, above the head, which it temporarily conceals. The end of this membrane terminates in two conical points which appear to be covered with a glutinous secretion, and at the same time an ovipositor of a somewhat similar character, but only semi-transparent, is pushed forward from the genital orifice. This latter is a tube, within which is the egg. As the ovipositor projects it turns itself inside out, like the finger of a glove, leaving the egg protruded at the end and lying between the two finger-like points of the membrane. The membrane and the ovipositor are then withdrawn each from the other. The egg adheres to the former, which collapses through the withdrawal of its contents, dragging the head forward and depositing it on the top of the head. Neither legs, palpi, nor the organs of the mouth take any part in oviposition, but after the collapse of the membrane the palpi are closed and the head is raised, by which action the egg is pushed forward to the front edge of the shield, forming in time an adherent mass of eggs, which are deposited in front of the tick.”
[The egg gives rise to the larval form, the so-called “seed-tick” stage. At first these minute specks are pallid and soft, but they soon harden and darken in colour. These larvæ are six-legged and crawl up grasses and various plants, and there await a passing host, waving their two front legs in the air and becoming attached by this means. The larval ticks feed upon the blood of the host, and when replete fall to the ground, the body becoming inflated in the meanwhile. These larvæ may remain on the host only two days, or they may remain much longer. Eventually they moult on the ground and change to the nymph or pupal stage, which has four pairs of legs. This pupa acts just as the larva, crawls up plants and waits to regain the host. After a time the nymphs, having gorged themselves with blood, fall off and remain on the ground for nearly three months; they then moult and become adult males and females. In about ten days they assume their normal colour and regain the host afresh; the female gradually swells until she attains that large inflated form so characteristic of ticks. The male does not swell, but nevertheless feeds upon the host and fertilizes the female.
[The act of coitus is strange: the male tick inserts its rostrum and other mouth organs into the sexual orifice of the female, between the base of the posterior pair of legs. The males then die and the females fall to the ground and deposit the ova. There are variations in the different species, of course, from those given above, which apply solely to Ixodes reduvius. The larvæ and nymphs seem to attack most animals, but the adults mainly keep to the same host. The periods in the life-cycle of ticks not only vary in the different species, but in each species according to climatic conditions; for instance, in the bont tick (Amblyomma hebræum, Koch), Lounsbury has shown that the development is rapid in summer, slow in winter. The period from the time that the female drops to the time she commences to lay eggs varied in specimens observed by him from twelve days in summer to twelve weeks in winter, and the complete period from the dropping of the female to the hatching of the eggs, from eleven weeks in summer to thirty-six weeks through the winter. Other stages vary in a similar manner.
[Ticks may live a long time away from the host provided they are supplied with a certain amount of moisture. Mr. Wheler kept dog ticks (Ixodes plumbeus) in the larval stage for ten months; the pupæ, male and female, of I. reduvius for six months.
[I have kept Ornithodorus moubata alive for eighteen months without food.
[In many species moulting takes place off the host, but in I. bovis, now known as Rhipicephalus annulatus, Say (the carrier of Texas fever), moulting takes place on the host, and in many other species also.337 Some species of ticks leave their host on its death (as the dog tick, Hæmaphysalis leachi), but others die with the host (bont tick, Amblyomma hebræum).
[Two species are of special importance, namely Ornithodorus moubata, Murray, which may infect human beings with the spirillum of African tick fever, and Dermatocentor reticulatus var. occidentalis, which is said to be the carrier of Rocky Mountain spotted fever.
Classification of Ixodidæ.
[The ticks, or Ixodidæ, are divided into two groups, known as (1) Argantinæ, (2) Ixodinæ. The Argantinæ are told from the Ixodinæ by the absence of dorsal or ventral shields in both sexes, and also by the rostrum being placed beneath the cephalothorax, which covers it over: except in the larval stage, in which it is subterminal, and in the pupal, when it partly projects. Legs nearly equal in length. The sexual orifice is situated between the two first pairs of legs. The males usually smaller than the females.
[The Ixodinæ have the legs unequal, of six segments with two false segments, making them look as if composed of eight segments. The rostrum is terminal and never hidden beneath the body. The sexual orifice is situated between the bases of the first three pairs of legs. In the males the orifice is obsolete or very rudimentary, sexual intercourse being effected by the rostrum. The males are smaller than the females. The shield in the females never covers so much as one-half of the body even when fasting, also in the larvæ and nymphs; but in the males, which do not distend, the shield covers the body entirely, or all but a narrow margin. The Ixodinæ are divided into two groups: (i) the Ixodæ, and (ii) the Rhipicephalæ. The former have a long proboscis reaching nearly to the end of the palpi or even a little longer than the palpi. The palpi are longer than broad. The Rhipicephalæ have short palpi, nearly or quite as broad as long, more or less conical or subtriangular. They were called Conipalpi by Canestrini.
Synopsis of Genera.