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1715, in which year was published his Address to Persons of Quality and Estate, containing suggestions for the establishment of special hospitals, schools and theological colleges, many of his proposals being afterwards carried into effect. Nelson married a Roman Catholic, Lady Theophila Lucy, daughter of the earl of Berkeley, and widow of Sir Kingsmill Lucy of Broxbourne.

See Charles F. Secretan, Memoirs of the Life and Times of the Pious Robert Nelson (1860); Thomas Birch, Life of Tillotson (2nd ed., 1753); Thomas Lathbury, History of the Nonjurors (1845).

NELSON, a river of Keewatin district, Canada, discharging the waters of Lake Winnipeg in a north-easterly direction into Hudson Bay. It drains an area of 360,000 sq. m. and, including its tributary the Saskatchewan, is 1450 m. long. It is navigable for small steamers for a distance of about 80 m., after which it is unnavigable except for canoes. It has a total fall between the lake and sea of 710 ft. Here its chief tributary is the Burntwood. Norway House at its source and York Factory at its mouth are important stations of the Hudson's Bay Company.

NELSON, a town of British Columbia, situated on the west arm of Kootenay lake. Pop. (1906) about 5000. It is the commercial, administrative and railroad centre of the east and west Kootenay districts. It is the northern terminus of a branch of the Great Northern railway and is also connected by rail and steamboat with the main line of the Canadian Pacific railway at Revelstoke and with the Crow's Nest line of the same system at Kootenay landing. It has direct railway communication with Rossland, Grand Forks and Greenwood.

NELSON, a municipal borough in the Clitheroe parliamentary division of Lancashire, England, 324 m. N. from Manchester by the Lancashire & Yorkshire railway. Pop. (1891) 22,754, (1901) 32,816. It is of modern growth, possessing a town hall, market hall, free library, technical school, pleasant park and recreation grounds, and an extensive system of electric tramways and light railways, connecting with Burnley and Colne. Its chief manufacture is cotton. It was incorporated in 1890, and the corporation consists of a mayor, 6 aldermen and 18 councillors. Area, 3466 acres.

many systematists united with the Acanthocephala and the
Nematomorpha to form the group Nemathelminthes.
The Nematoda possess an elongated and thread-like form (sec
fig. 1), varying in length from a few lines up to several feet. The
body is covered externally by a chitinous cuticle which is a
product of the subjacent epidermic layer in which no cell limits
can be detected though nuclei are scattered through it. The
cuticle is frequently prolonged into spines and papillae, which
are especially developed at the anterior end of the body. The
mouth opens at one extremity of the body and the anus at or
near the other. Beneath the epidermis is
a longitudinal layer of muscle-fibres which
are separated into four distinct groups
by the dorsal, ventral and lateral areas;
these are occupied by a continuation of the
epidermic layer; in the lateral areas run
two thin-walled tubes with clear contents,
which unite in the anterior part of the
body and open by a pore situated on the
ventral surface usually about a quarter
or a third of the body length from the
anterior end. These vessels are the nitrogen-
ous excretory organs. The body-cavity is
largely occupied by processes from the large
muscle celis of the skin. These processes
stretch across the body cavity to be inserted
in the dorsal and ventral middle lines.

The body-cavity also contains the so-
called phagocytic organs. These consist
of enormous cells with nuclei so large as
to be in some cases just visible to the naked
eye. These cells are disposed in pairs,
though the members of each pair are not
always at the same level. The number of
cells is not large (some 2 to 8), and as a
rule they lie along the lateral lines. In
some species (Ascaris decipiens) the giant
cell is replaced by an irregular mass of
protoplasm containing a number of small
nuclei. Such a plasmodium bears, on its
periphery, groups of rounded projections
of protoplasm termed end-organs. Similarly
the giant cells are produced at their peri-

NELSON, a seaport of New Zealand, the seat of a bishop and capital of a provincial district of the same name; at the head of Blind Bay on the northern coast of the South Island. Pop. (1906) 8164. The woods and fields in the neighbourhood abound with English song-birds, and the streams are stocked with trout; while the orchards in the town and suburbs are famous for English|phery into a number of branching prokinds of fruit, and hops are extensively cultivated. The town possesses a small museum and art gallery, literary institute, government buildings, and boys' and girls' schools of high repute. The cathedral (Christ Church) is finely placed on a mound which was originally intended as a place of refuge from hostile natives. It is built of wood, the various native timbers being happily combined. Railways connect the harbour with the town, and the town with Motupiko, &c. The harbour, with extensive wharves, is protected by the long and remarkable Boulder Bank, whose southern portion forms the natural breakwater to that anchorage. The settlement was planted by the New Zealand Company in 1842. The borough returns one member to the house of representatives, and its local affairs are administered by a mayor and council.

NELSONVILLE, a city of Athens county, Ohio, U.S.A., on the Hocking river, 62 m. S.E. of Columbus. Pop. (1890) 4558, (1900) 5421, including 328 foreign-born and 204 negroes; (1910) 6082. Nelsonville is served by the Hocking Valley railway. The city is in one of the most productive coal sections of the state; there are large quantities of clay in the vicinity; and the principal industries are the mining and shipping of coal and the manufacture of fire-clay products. Nelsonville was settled in 1818 and was incorporated in 1838; it was named in honour of Elisha Nelson, who built the first house here.

NEMATODA, in zoology, a group of worms. The name Nematoda (Gr. vua, thread, and eldos, form) was first introduced by Rudolphi, but the group had been previously recognized as distinct by Zeder under the name Ascarides. They are now by

cesses which bear similar end-organs on
their surface and in some cases terminate
in them. These end-organs are the active
agents in taking up foreign granules, or
bacteria, which may have found their way
into the fluid of the body-cavity. From
the shape and position of the phagocytic
organs it is obvious that they form admir-
able strainers through which the fluid of
the body-cavity filters (figs. 2, 3).

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s,

Opening of seg

mental tubes

(placed by mis

take on the dorsal instead of the ventral surface).

The alimentary tract consists of a straight tube running from the mouth to the anus without any convolutions; it is separable into three divisions: (1) a muscular ocsophagus, which is often provided te, Testes. with cuticular teeth; (2) a cellular intes- cd. Vas deferens. tine, and (3) a short terminal rectum sp. Cloaca. surrounded by muscular fibres. Neither pa, Papillae. here nor elsewhere are cilia found at any period of develop ment.

A nervous system has been shown to exist in many species, and consists of a perioesophageal ring giving off usually six nerves which run forwards and backwards along the lateral and median lines; these are connected by numerous fine, circular threads in the sub-cuticle. Some of the free-living forms possess eye specks. The sexes are distinct (with the exception of a few forms that are hermaphrodite), and the male is always smaller than the female. The generative organs consist of one or two tubes, in the upper

portion of which the ova or spermatozoa are developed, the lower | portion serving as an oviduct or vas deferens; the female generative organs open at the middle of the body, the male close to the posterior extremity into the terminal portion of the alimentary canal; from this cloaca a diverticulum is given off in which are developed one to three chitinous spicules that subserve the function of copulation. The spermatozoa differ from those of other animals in having the form of cells which sometimes perform amoeboid movements. Most remarkable sexual conditions are found to occur in the free-living genera Rhabditis and

6

FIG. 2.-Sclerostomum armatum, 9, X about 31, opened to show the phagocytic organs. (From Nassonov.)

1, Mouth.

2, Anterior end of alimentary canal.

3. Posterior end of alimentary canal.

4. Ovary.

FIG. 3. One of the phagocytic organs of Sc. armatum, highly magnified. (From Nassonov.) 5. 6 and 7, Anterior middle and 1, Nucleus of giant-cell. posterior pairs of phago- 2, One of the processes and endcytic organs. organs of the same. Diplogaster. While some of the species are bisexual, others are protandrous, self-fertilizing hermaphrodites. In cultures of the latter there occur very rare supplemental males which appear in no sense degenerate but as fit for reproduction as the males of the bisexual species. Though possessing a complete copulatory apparatus and producing large quantities of spermatozoa, they have lost their sexual instinct and play no part in the economy of the species. These psychically decadent" individuals appear to represent the entire male sex of a bisexual species, and become unnecessary owing to the grafting of hermaphrodit

ism on the female sex.

Mode of Life and Metamorphoses.-While the majority of the

Nematodes are parasites, there are many that are never at any period of their life parasitic. These free-living forms are found everywhere-in salt and fresh water, in damp earth and moss, and among decaying substances; they are always minute in size, and like many other lower forms of life, are capable of retaining their vitality for a long period even when dried, which accounts for their wide distribution; this faculty is also possessed by certain of the parasitic Nematodes, especially by those which lead a free existence during a part of their life-cycle. The freeliving differ from the majority of the parasitic forms in undergoing no metamorphosis; they also possess certain structural peculiarities which led Bastian (Trans. Linn. Soc., 1865) to separate them into a distinct family, the Anguillulidae. It is impossible, however, to draw a strict line of demarcation between the free and parasitic species, since-(1) many of the so-called free Nematoda live in the slime of molluscs (Villot), and are therefore really parasitic; (2) while certain species belonging to the freeliving genus Anguillula are normally parasitic (e.g. A. tritici, which lives encysted in ears of wheat), other species occasionally adopt the parasitic mode of existence, and become encysted in slugs, snails, &c.; (3) it has been experimentally proved that many normally parasitic genera are capable of leading a free existence; (4) transitional forms exist which are free at one period of their life and parasitic at another. The parasitic Nematodes include by far the greatest number of the known genera; they are found in nearly all the orders of the animal kingdom, but more especially among the Vertebrata, and of these the Mammalia are infested by a greater variety than any of the other groups. Some two dozen distinct species have been described as occurring in man. The Nematode parasites of the Invertebrata are usually immature forms which attain their full development in the body of some vertebrate; but there are a number of species which in the sexually adult condition are peculiar to the Invertebrata.

The Nematoda contain about as many parasitic species as all the other groups of internal parasites taken together; they are found in almost all the organs of the body, and by their presence, especially when encysted in the tissues and during their migration from one part of the body to another, give rise to various pathological conditions. Although some attain their full development in the body of a single host-in this respect differing from all other Entozoa-the majority do not become sexually mature until after their transference from an "intermediate" to a "definitive" host. This migration is usually accompanied by a more or less complete metamorphosis, which is, however, not so conspicuous as in most other parasites, e.g. the Trematoda. In some cases (many species of Ascaris) the metamorphosis is reduced to a simple process of growth.

The parasitic and free-living Nematodes are connected by transitional forms which are free at one stage of their existence and parasitic at another; they may be divided into two classesthose that are parasitic in the larval state but free when adult, and those that are free in the larval state but parasitic when adult.

(1) To the first class belong the so-called " hairworm," Mermis, not to be confused with the Gordian worms. The adult forms of M. nigrescens live in damp earth and may be seen after storms or early in the morning crawling up the stalks of plants, a fact which causes people to talk about showers of worms. The eggs are laid on

Ercolani successfully cultivated Oxyuris curvula, Strongylus armatus and other species in damp earth; the free generation was found to differ from the parasitic by its small size, and by the females being ovoviviparous instead of oviparous. To this phenomenon he gave the name of dimorphobiosis.

The genera Ascaris, Filaria, Trichosoma are found throughout the Vertebrata; Cucullanus (in the adult condition) only in fishes and Amphibia; Ankylostoma, Trichocephalus, Trichina and Pseudalius live only in the Mammalia, the last-mentioned genus being confined to the order Cetacea; Strongylus and Physaloptera are peculiar to mammals, birds and reptiles, while Dispharagus, Syngamus and Hystrichis are confined to birds. Mermis in the larval state) is confined to the Invertebrata and Sphaerularia to bees. Oxyuris, Amphibia and one or two insects. Dacnitis and Ichthyonema are though chiefly parasitic in the Mammalia, occurs also in reptiles, only found in fishes.

See NEMATOMORPHA.

the ground and the young larvae make their way into grasshoppers, Swine become infested with Trichinella in this way and also by eating in whose bodies they pass most of their larval life. (2) To the second the dead bodies of rats, and the parasite is conveyed to the body of class belong Ankylostoma, Strongylus and many species of Ascaris; man along with the flesh of " trichinized swine." the embryo on leaving the egg lives free in water or damp earth, and Importance in Pathology.--Among recent advances having resembles very closely the free-living genus Rhabditis. After a longer or shorter period it enters the alimentary canal of its proper host with medical import in our knowledge of the Nematodes, the chie drinking-water, or it bores through the skin and reaches the blood- are those dealing with the parasites of the blood. F. bancrofti iz vessels, and is so conveyed through the body, in which it becomes known to live in the lymphatic glands, and its embryos Microsexually mature. Rhabditis nigrovenosa has a developmental history filaria sanguinis hominis nocturna, passing by the thoracic duct, which is entirely anomalous, passing through two sexual genera- reach the blood-vessels and circulate in the blood. Manson tions which regularly alternate. The worm inhabits the lung of the frog and toad, and is hermaphrodite (Schneider) or partheno- showed in 1881 that the larvae (Microfilariae) were not at all genetic (Leuckart); the embryos hatched from the eggs find their times present in the blood, but that their appearance had a way through the lungs into the alimentary canal and thence to the certain, periodicity, and the larvae of F. bancrofti. Microfilaria exterior; in a few days they develop into a sexual larva, called a nocturna swarmed in the blood at night-time and disappeared Rhabditiform larva, in which the sexes are distinct; the eggs remain within the uterus, and the young when hatched break-through its from the peripheral circulation during the day, hiding away in walls and live free in the perivisceral cavity of the mother, devouring the large vessels at the base of the lungs and of the heart. Ten the organs of the body until only the outer cuticle is left; this eventu- years later Manson discovered a second species, Filaria perstans, ally breaks and sets free the young, which are without teeth, and whose larvae live in the blood. They, however, show no periodhave therefore lost the typical Rhabditis form. They live for some time in water or mud, occasionally entering the bodies of water icity, and are found continuously both by day and by night; snails, but undergo no change until they reach the lung of a frog, and their larval forms are termed Microfilaria perstans. The when the cycle begins anew. Although several species belonging to adult stages are found in the sub-peritoneal connective tissue. the second class occasionally enter the bodies of water snails and A third form, Microfilaria diurna, is found in the larval stage in other animals before reaching their definitive host, they undergo no alteration of form in this intermediate host; the case is different, blood, but only in the daytime. The adult stage of this form is however, in Filaria medinensis and other forms, in which a free the Filaria loa found in the subcutaneous tissues of the limbs. larval is followed by a parasitic existence in two distinct hosts, all The presence of these parasites seems at times to have little the changes being accompanied by a metamorphosis. Filaria medi- effect on the host, and men in whose system it is calculated nensis-the Guinea worm-is parasitic in the subcutaneous connective tissue of man (occasionally also in the horse). It is chiefly there are some 40-50 million larvae have shown no signs of found in the tropical parts of Asia and Africa, but has also been disease. In other cases very serious disorders of the lymphatic met with in South Carolina and several of the West Indian islands. system are brought about, of which the most marked is perhaps The adult worm in the female sometimes reaches a length of 6 ft. Elephantiasis. Manson and Bancroft suggested that the second The males have only recently been discovered. The female is viviparous, and the young, which, unlike the parent, are provided with host of the parasite is the mosquito or gnat, and for a long time it a long tail, live free in water; it was formerly believed from the was thought that they were conveyed to man by the mosquito frequency with which the legs and feet were attacked by this parasite dying after laying her eggs in water, the larval nematodes that the embryo entered the skin directly from the water, but it escaping from her body and being swallowed by man. It is has been shown by Fedschenko, and confirmed by Manson, Leiper and others, that the larva bores its way into the body of a Cyclops now held that the parasite enters the blood of man through the and there undergoes further development. It is probable that the piercing mouth-parts at the time of biting. When first sucked parasite is then transferred to the alimentary canal of man by means up by the insect from an infected man it passes into its stomach, of drinking-water, and thence makes its way to the subcutaneous and thence makes its way into the thoracic muscles, and there connective tissue. for some time it grows. Next the larvae make their way into the connective tissue in the pro-thorax, and ultimately bore a channel into the base of the piercing apparatus and come to rest between the hypopharynx and the labium. Usually two are found in this position lying side by side; it would be interesting (1) In the former class the eggs are extruded with the faeces, and to know if these are male and female. From their position in the young become fully formed within the egg, and when accidentally the proboscis the larvae can easily enter the blood of man the swallowed by their host are liberated by the solvent action of the next time the mosquito bites (Low, Brit. Med. Journ., June 1900; gastric juice and complete their development. This simple type of life-history has been experimentally proved by Leuckart to be James, ibid., Sept. 1900). Shortly after Low had published his characteristic of Trichocephalus affinis, Oxyuris results, Grassi and Noè issued a paper dealing with the larvae ambigua and other species. (2) The life-history of F. immitis, which is spread by means of the mosquito Anopheles of Ollulanus tricuspis is an example of the second (Centrbl. Bakter. I. Abth. xxviii., 1900). The larvae of this class. Ollulanus tricuspis is found in the adult parasite develop in the Malpighian tubules of the insect; at a state in the alimentary canal of the cat; the young worms are hatched in the alimentary certain stage they cast their cuticle and make their way into canal, and often wander into the body of their the space-part of the haemocoel-found in the labium. During host and become encysted in the lungs, liver and the act of biting the labium is bent back, and as the piercing other organs; during the encystment the worm stylets enter the skin of the sufferer this bending becomes more degenerates and loses all trace of structure. This wandering appears to be accidental, and to and more acute. Grassi and Noè think that if the cavity of the have nothing to do with the further evolution labium be full of the larval nematodes this bending will burst the of the animal which takes place in those embryos tissue, and through the rent the larvae will escape and make their which are voided with the excrement. Leuckart way into the body of the host. Besides Anopheles, two species proved experimentally that these young forms become encysted in the muscles of mice, and of Culex, C. penicillaris and C. pipiens, are also accused of transthe cycle is completed after the mouse is de-mitting the larvae. A paper by Noè (Atti Acc. Lincei, ix., 1900) voured by a cat. The well-known Trichinella seems to prove beyond doubt that the larvae of F. immitis spiralis (fig. 4) has a life-history closely resembl are transmitted in the manner indicated. The adult worm is ing that of Ollulanus. The adult worm, which FIG. 4.-Trichin is of extremely minute size, the male being only encystedth and the female of an inch in length among muscular inhabits the alimentary canal of man and many fibres. (After other carnivorous mammalia; the young bore Leuckart.) their way into the tissues and become encysted in the muscles within the muscle-bundles according to Leuckart, but in the connective tissue between them according to Chatin and others. The co-existence of the asexual encysted form and the sexually mature adult in the same host, exceptionally found in Ollulanus and other Nematodes, is the rule in Trichinella; many of the embryos, however, are extruded with the faeces, and complete the life cycle by reaching the alimentary canal of rats and swine which frequently devour human ordure

The Nematoda which are parasitic during their whole life may similarly be divided into two classes-those which undergo their development in a single host, and those which undergo their development in the bodies of two distinct hosts.

ella

chiefly found in the heart of the dog, and usually in the right side, which may be so packed with the worms as seriously to interfere with the circulation (fig. 5). The females produce thousands of larvae, which circulate in the blood, and show a certain periodicity in their appearance, being much more numerous in the blood at night than during the day. increased

Importance as Pests.-Agriculturists now pay attention to the nematodes that destroy their crops. A good example of a fairly typical case is afforded by Heterodera schachtii, which attacks beetroot and causes great loss to the Continental sugar manufacturers. The young larvae, nourished by the yolk

[graphic]

which remains over from the egg and by the remains of the | 300 embryos, and that half of these are females, the number of mother which they have taken into their alimentary canal, descendants would be, after six generations, some 22,781 milliards make their way through the earth, and ultimately coming across (A. Strubell, Bibl. Zool., 1888-1889). Other species which have the root of a beet, begin to bore into it. This they do by means been recorded in the United Kingdom are Tylenchus devastatrix of a spine which can be protruded from the mouth. Once within (Kuhn), on oats, rye and clover roots; T. tritici, causing the the root, they absorb the cell sap of the parenchyma and begin to swell until their body projects from the surface of the root in non.boold ad

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FIG. 5.

A, View of the heart of a dog infested with Filaria immitis Leidy; the right ventricle and base of the pulmonary artery have been opened: a, aorta; b, pulmonary artery; c, vena cava; d, right ventricle; e, appendix of left auricle: f, appendix of right auricle.

B, Female F. immitis, removed from the heart to show its length. the form of a tubercle (fig. 6). The reproductive organs do not begin to appear until the larva has twice cast its skin. After this a marked sexual dimorphism sets in. The female, hitherto indistinguishable from the male, continues to swell until she attains the outlines of a lemon. Doing this she bursts the epidermis of the rootlet, and her body projects into the surrounding earth. The male has a different life-history (fig. 7). After the second larval moult, he passes through a passive stage comparable to the pupa-stadium of an binsect, and during this stage, which occurs inside the root, the reproductive organs are perfected. The male next casts his cuticle, and by means of his spine bores through the tissues of the root and escapes A,a,Female Heterodera schachtii Schmidt, into the earth. Here breaking through the epidermis of a root; the head is still embedded in the parenhe seeks a female, chyma of the root. pairs, and soon afterB, a, larvae boring their way into a root; wards dies. The eggs b, larva of the immobile kind surrounded by the old skin, living as an ectoparasite of the female give on the outside of the root. (From Strubell.) rise to embryos within the body of the mother; her other organs undergo a retrogressive change and serve as food for the young, until the body-wall only of the mother remains as a brown capsule. From this the young escape and make their way through the earth to new roots. The whole life-history extends over a period of some 4-5 weeks (fig. 7), so that some 6-7 generations are born during the warmer months. If we assume that each female produces

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FIG. 7.

schachtii,

m, Muscles moving spicule. n, Spicule.

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ear-cockle of wheat; Cephalobus rigidus (Schn.), on oats; Heterodera radicicola (Greef), on the roots of tomatoes, cucumbers, potatoes, turnips, peach-trees, vines and lettuce, and many other plants.

See N. Nassonov, Arch. Mikr. Anat. (1900); Arch. parasit. (1898): Rabot, Lab. Warsaw (1898); Zool. Ans. (1898); Jägerskiold, Centrbl. Bakter. (1898); J. Spengel, Zool. Ans. (1897); H. Ehlers, Arch. Naturg. (1899); O. Hamann, Die Nemathelminthen (1895). (F. E. B.; A. E. S.)

NEMATOMORPHA. This zoological group includes Gordian worms which are found swimming in an undulatory manner or coiling round water-weeds in ponds and puddles, or knotted together in an apparently inextricable coil. They may be several inches in length and are no thicker than a piece of whip-cord.

The male is distinguishable from the female by the presence of a fork at the posterior end of the body. The body is covered by a cuticle which is sculptured and the various markings are of systematic importance: it is secreted by a hypodermis which also includes nerve-cells and some gland-cells. In the adult aquatic stage the alimentary canal shows signs of degeneration, and it seems probable that in this stage Gordian worms take no food. The mouth is terminal or subterminal; there is a weak sucking pharynx situated behind the brain, and a long intestine lying along the medio-ventral body-cavity; it ends in a cloaca which receives the vasa deferentia in the male. There is a single unsegmented nerve-cord which runs along the ventral middle line and enlarges posteriorly into a caudal ganglion and anteriorly in a ganglion, the brain, which is not supra-oesophageal. The peripheral nervous system is minutely described by T. H. Montgomery. There is a median eye on the head.

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NEMERTINA

The Nematomorpha are nearly solid,quite so at each end, gon nhau of 73741809 blazinggesid

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impossible to connect them with the Annelida. Until more is known
it seems wisest to look upon them as an isolated assemblage of
animals with no near affinities to any of the great phyla.

LITERATURE.-L. Camerano, "Monografía dei Gordii," Mem. Acc.
Torino, xlvii. (1897), contains literature; O. von Linstow, Arch.
mikr. Anat., li. (1898); T. H. Montgomery, Bull. Mus. Harvard,
xxxii. (1898); Amer. Natural., xxxiii. (1899); Zool. Jahrb.. Anal.,
xviii. (1903) p. 387; F. Vejdovsky, Zeitschr. wiss. Zool., Ivii. (1894):
(A. E. S.)
A. Villot, Arch. Zool. exp. ii. (1887); C. R. Ac. Sci., cviii. (1889);
H. B. Ward, Bull. Mus. Harvard, xxiii. (1892).

NEMERTINA, or NEMERTEANS (Nemertea), a subdivision of
worms, characterized by the ciliation of the skin, the presence
of a a retractile proboscis, the simple arrangement of the generative
apparatus, and in certain cases by a peculiar pelagic larval
om stage to which the name "pilidium " has been given. Many of
them are long thread-shaped or ribbon-shaped animals, more or
Even the comparatively
less cylindrical in transverse section.
shortest species and genera can always be termed elongate, the
broadest and shortest of
Malacobdella and
all being the parasitic
pelagic Pelagonemertes.
There are no exterior
appendages of any kind.
The colours are often

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From Cambridge Natural History, vol. ii, "Worms, "&c., by permission of Macmillan

&Co., Ltd.

FIG. 1-A water plant around which a female Gordius is turning and laying eggs. a, a, clump and string of eggs.

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and only in the middle region of the body are there any body-
cavities, the space within the body being usually filled up with
parenchyma. There are four closed spaces of the nature of
body-cavities, two lateral and a dorso-median and a ventro-
median. Into the former the ovaries project, though the lumen
of the lateral body-cavity is quite shut off from the lumina of
the ovaries or uteri. In the adult male
the lateral body-cavities are absent. A
curious duct with lateral branches termed
the supra-intestinal organ lies above the
intestine in the female. There are two
series of ovaries extending through a large
part of the body and accompanied by two
uteri; the latter open by two oviducts
which debouch into an atrium which also

receives the intestine and a single recep-
taculum seminis, and is continued back-
ward as the cloaca; this opens posteriorly.
The ovaries are epithelial sacs which open
into the uteri. The paired testes extend
through the greater part of the body and
end in two vasa deferentia which unite
with the intestine to form a cloaca.
The eggs are laid in the spring as a rule,
From Cambridge Natural
History, vol. ii, "Worms,"
&c., by permission of Mac- and after about a week they give rise to a
millan & Co., Ltd.
FIG. 3.-Tarsal joint minute, ringed larva with a protrusible
of an Ephemerid larva boring apparatus consisting of three
into which two Gordius chitinous rods. By the aid of this the
(a,a) have larva makes its way into the soft body
larvae,
penetrated. Magnified.
of some insect larva, Ephemerids, Chiro-
nomids, or even of Molluscs, and encysts in the muscles or fat
body. The insect, which may have become an imago with the
Gordian larva still in it, is then eaten by a carnivorous insect
or by a fish, and the contained Gordian larva becomes elongate
and mature in its second host. After a year or more this larva
emerges into the water and commences to reproduce.

The unexpected occurrence of these worms in pools and puddles, often in great numbers, has given rise to myths about showers of worms. They occasionally make their way into the human stomach with the drinking-water and are vomited; but this is a case of pseudo-parasitism-they are no true parasite of man.

There are a considerable number of species divided among the four genera: Gordius, Paragordius, Chordodes and Parachordodes; the last, a genus of Camerano's, is looked upon with some doubt by Montgomery. A free swimming marine form with longitudinal rows of bristles, known as Nectonema A. E. Verrill, may also come here. but at present its life-history is unknown. The Nematomorpha form an isolated group; at first sight they seem to be connected with the Nematoda, but in reality their only common feature is the tubular genitalia opening into a cloaca, and it scems at present

the

very bright and varied.
Nemertines live in the
sea, some being common
amongst the corals and
algae, others hiding in
the muddy or sandy
bottom, and secreting
gelatinous tubes which
ensheath the body along
its whole length. For-
ally arranged amongst
merly, they were gener-
the Platyelminthes as
a sub-order in the
order of the Turbel-
larians, but with the
advance of our know-
ledge of these lower

worms it has been found
to separate
desirable
them from the Turbel-

the Nemertina as

larians and to look upon

a

O. Bürger classifies
into four
Nemertines
separate phylum.

orders:

[blocks in formation]

I. Protonemertini, in
which there are two layers anus.
of dermal muscles, ex-
ternal circular and in-

Families, ternal longitudinal; the nervous system lies external to the circular has no stylet; there is no caecum to the intestine. CARINELLIDAE, HUBRECHTIIDAE. muscles; the mouth lies behind the level of the brain; the proboscis

11. Mesonemertini, in which the nervous system has passed into the dermal muscles and lies amongst them; other characters as in Protonemertini. Family, CEPHALOTHRICIDAE.

III. Metanemertini, in which the nervous system lies inside the dermal muscles in the parenchyma; the mouth lies in front of AMPHIPORIDAE, PROSORHOCMIDAE, the level of the brain; the proboscis as a rule bears stylets; the OTOTYPHLONEMERTIDAE, TETRASTEMMATIDAE, NECTONEMERTIDAE, PELAGONEMERTIDAE, intestine nearly always has a caecum. Families, EUNEMERTIDAE, MALACOBDELLIDAE.

This order represents the Hoplonemertini of Hubrecht.box IV. Heteronemertini, in which the dermal musculature is in longitudinal; the nervous system lies between the first and second no stylets on the three layers, an external longitudinal, a middle circular, an internal development; there is no intestinal caecum; of these layers; the outer layer of longitudinal muscles is a new EUPOLIIDAE. LINEIDAE. proboscis and the mouth is behind the level of the brain. Families,

Nemertes was a sea nymph, daughter of Nereus and Doris. One of the genera was named Nemertes by Cuvier.

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