Worms, or VERMES, a term destitute of scientific precision, but often applied to the members of numerous classes of invertebrate animals which are more or less earthworm-like in appearance. It is little more than a convenient name for a shape, for among the forms called 'worms' the variety of internal structure is so great that no common characters can be noted beyond the general occurrence of bilateral symmetry. The numerous classes include many types of much interest on account of the affinities which they present to other types of animals. The higher forms, known as Annelids, consist of a series of homologous segments; the lower forms are unsegmented. In the present state of our knowledge as to the affinities of 'worms,' all that can be attempted here is to give a catalogue of the various classes, arranged in a manner which cannot pretend to be more than provisional.
PLATHELMINTHES
OR
SCOLECIDA
(Flat-worms).
TURBELLARIA.—Small 'worms,' usually aquatic, often known as Planarians (q.v.)—e.g. Planaria, Convoluta, Vortex.
TREMATODA.—Parasitic 'flukes'—e.g. Distomum. See FLUKE.
CESTODA.—Parasitic 'tapeworms'—e.g. Taenia. See TAPEWORM.
NEMERTEA.—Free-living aquatic worms—e.g. Nemertes, Lineus. See NEMERTEA.
NEMATHELMINTHES
(Round-worms).
NEMATODA.—Thread-worms, some free, most parasitic—e.g. Ascaris (q.v.), Trichina (q.v.), Gordius. See THREAD-WORMS, &c.
ACANTHOCEPHALA.—Parasitic. Echinorhynchus (q.v.)
DISCOPHORA, or HIRUDINEA. Leeches—e.g. Hirudo. See LEECHES.
CHETOPODA.—Bristle-footed Annelids. (1) Oligochaeta—Earthworms (q.v.); (2) Polychaeta—marine worms, both free-swimming and sedentary—e.g. Nereis, Aphrodite (see SEA-MOUSE), Arenicola (Lobworm), Serpula; (3) Echinirida, bristly 'Gephyreans'—e.g. Echinurus, Bonellia. Related types, (a) Archiannelida—primitive forms—e.g. Polygordius, and (b) Myzostomata, parasitic on Crinoids.
ANNELIDA .....
Incerte sedis, perhaps related to Chaetopods—(1) Chaetognatha—e.g. Sagitta (q.v.), (2) Rotatoria (q.v.), or Rotifera.
SIPUNCULOIDEA—e.g. Sipunculus (q.v.).
PHORONIDEA—Phoronis.
POLYZOA, or BRYOZOA. See SEA-MAT.
BRACHIOPODA (q.v.), or LAMP-SHELLS.
VERMES INCERTE
SEDIS.
Worms as a Disease of Childhood.—The articles dealing with Ascaris, Cestoid Worms, Tapeworm, Thread-worms, Parasitic Animals, and Vernifuges treat of the natural history of the worms infesting the human subject, and of the remedies to be employed for their expulsion, so here need only be noticed the symptoms which are usually considered to be indicative of the presence of worms in children. These symptoms are, however, in reality, only evidence of irritation of the mucous membrane of the intestinal canal, which may be due to other causes than worms, as, for instance, the presence of indigestible matter, unhealthy secretions, or the existence of a morbid condition of the membrane itself. 'Perhaps few of the symptoms—and they are very numerous—which are found while worms exist in the body can be directly attributed to the presence of these parasites, as they may all of them, or nearly all, be found also in cases where repeated purgatives have convinced us that worms are absent. They are therefore probably due in great part to the abdominal derangement which favours the development of the entozoa' (Eustace Smith, Wasting Diseases of Children, 4th ed. p. 231). Although then the symptoms commonly referred to the presence of worms may exist without them, yet there is a group of symptoms which, when occurring together, should, at all events, excite our suspicions. These symptoms are divisible into two groups. The first, those dependent directly on the presence of worms in the intestines, comprise loss of flesh; appetite capricious, sometimes excessive; pain or discomfort in the abdomen; irregular action of the bowels and much mucus, sometimes blood, in the stools. The second group comprises the symptoms connected with the sympathetic relations of the digestive organs, and due to some form of reflex nervous action, and amongst the most marked of them are those of the head. The sleep becomes unquiet, and the little patient is liable to start up suddenly from slumber; grinding of the teeth is common; the pupils are often dilated, and there may be headache, and sometimes convulsions—symptoms painfully like those of Hydrocephalus (q.v.), but often disappearing on the expulsion of worms. Itching of the nose is frequently present. A dry cough, unaccompanied by any signs of disease of the thoracic organs, is regarded as a sympathetic or reflex symptom of worms; and vomiting and hiccough often accompany their presence.
The Round-worm (Ascaris lumbricoides) may be present in the small intestine (its ordinary seat) in large numbers without occasioning any disturbance; but when symptoms are present the most prominent are sharp colicky pains about the navel, nausea, faintness, and other nervous disturbances. The Tapeworm (Tænia) may also cause pain in the belly; emaciation is sometimes very marked, but reflex disturbances are less common than in the case of round-worms. The Thread-worm (Oxyuris vermicularis) chiefly occurs in the large intestine, where it often exists in large numbers, looking like bits of cut thread. In a recently voided stool they are seen to be in rapid motion; hence they are called Ascarides (from the Greek askaridzetin, 'to jump'), and hence also, in all probability, the great local irritation which they occasion as compared with the quiet round-worms. The characteristic sign of the presence of these thread-worms is the itching and irritation felt at the anus. Other parasitic worms, as Bilharzia, Guinea-worm, and Trichina, are separately discussed. The worms by which Herod was eaten are interpreted to mean a kind of lice (Pediculus tabescentium; see LICE), credited with multiplying with awful rapidity and burrowing in the flesh.
The 'worms' implied in worm-eaten furniture or books are rather insects or their grubs; see BARK-BEETLES, BOOKWORM, BORERS, BORING-ANIMALS.
The Worms of the Dog belong principally to the two classes Nematoda or round-worms and Cestoda or tapeworms. The commonest round-worm is Ascaris marginata, infesting stomach and intestines; Dochmius trigonocephalus, also found there, and Tricocephalus depressieulus, or whip-worm (in the cæcum), are of less importance. Other round-worms are Filaria immitis, found in the heart, and Strongylus gigas in the kidneys. The latter, though the largest of the Nematodes, does not always cause inconvenience to the host; sometimes, however, there has been continual wasting of the flesh; in other instances great pain has been manifested by howling night and day; and in some instances the urine has contained blood or purulent matter, and the dog has been observed to walk with its body curved to the affected side when the worm is in one kidney only.
The tapeworms are well known to infest two hosts. In the herbivora they are found in the embryonic or cystic stage, and then appear as bladders containing fluid (bladder-worms). The most common in Britain are (1) Tænia cœnuri, which infests the intestines of the dog in its mature stage, whilst the cystic form, the Cœnurus cerebralis, is found in the brain of the sheep, sometimes that of cattle, very rarely in the brain of the horse. (2) Tænia serrata ('sawlike') is found in the larval or cystic form (cysticercus pisiformis) in the peritoneal cavity of hares and rabbits; these are eaten by the dog, and arrive at the mature stage in the intestines of that animal; the segments of the worm, as is the case with other tapeworms, are expelled with the faeces of the host, and the ova or eggs which they contain escape and are scattered over the grass, which is eaten by the herbivorous host, and there become hatched. (3) Tænia echinococcus is, in the mature stage, a very small tapeworm, but in its embryonic form it attains large dimensions, and is called the Echinococcus veterinorum, and is found in the liver, lungs, kidneys of man, the Ruminantia, and the pig. It is very prevalent and destructive to human life in Iceland. (4) Tænia cucumerina ('cucumber-shaped') is a small but long tapeworm, the segments of which when mature escape from the intestines and discharge their ova on the skin of the dog, and are there eaten by the dog-louse, Trichodectus latus, or dog-flea, Pulex seraticeps, in the bodies of which the ova are hatched and assume the cystic form. The fleas and lice irritate the skin of the dog, who in hunting for them with his teeth swallows some of them and the contained ova, which become hatched and assume the mature form in its intestines. In this way the presence of this tapeworm in sucking puppies is accounted for. (5) Tænia marginata is the largest tapeworm found in the dog, and is the mature form of the cysticercus tenuicollis which is found in the peritoneal, pleural, and even in the pericardial sac of various animals, particularly the Ruminants. In addition to the above the following Tænia are sometimes found in the dog: Tænia krabbei, T. serialis, and T. litterata; and another form of tapeworm, called the Bothriocephalus latus—which also exists in man—the cystic stage of which is found in fish, particularly the pike and burbot; and in Greenland a shorter species of this worm is found in the dog and once only in man. As to treatment, for tapeworms areca nut and the oil of the male shield fern, succeeded by a purgative, and for round-worms santonin, succeeded by a purgative, are the most reliable remedies.
A worm is found in the nasal cavities of the dog called Linguatula tænoides, and is classified under the Arachnida. Its presence causes irregular fits of sneezing, difficult inspirations, and a discharge of mucus, containing ova, from the nose.