Part 24

The Crustacea breathe by gills, and are therefore suited to an aquatic life. A few species, however, live in damp earth, or in places where the air is damp (wood lice). Crustacea have two pairs of antennæ, and a large number of appendages arranged in a characteristic way, but differing very much in shape in the different groups; skin usually hard and thick. Lobsters, crayfish, crabs, wood lice, and the small sand-hoppers, water-fleas, etc., belong to the Crustacea. No Crustacean is harmful agriculturally.

=Third Sub-Kingdom: VERMES= (WORMS).

Worms are bilaterally symmetrical animals, in which the body is enclosed in a “dermo-muscular tube.” Under the delicate epidermis there is found a layer, which does not, as in the higher animals, consist exclusively of dermis, but is partly composed of muscle-fibres, which form a distinct coat internally. Worms are able to move by contracting the various components of the dermo-muscular tube thus formed. In some worms limbs assist in the movements, but in others this is not so; in any case, however, the limbs play a relatively subordinate part. These limbs, which are only present in the bristle-worms, are small, always unjointed, foot-stumps, which bear bristles. Leeches and some other worms possess suckers by which they can attach themselves, and move by alternately contracting and extending their bodies.

Footnote 3:

In ordinary language one understands by “worms” elongated, cylindrical animals; and several insect larvæ (e.g. “wireworms,” p. 103) have the name applied to them. But to zoologists all “worm-shaped” animals are not worms, nor have all worms an elongated cylindrical shape (liver-fluke).

There are segmented and unsegmented worms (thread worms, liver-flukes); the degree of segmentation is also very various. In many tapeworms each joint may be regarded as an individual animal. The joints of other segmented worms (earthworms) do not become detached, like those of tapeworms, for the purpose of reproduction. The nervous system is absent in the lowest worms; in the higher worms ganglia always constitute its central parts, and in annelids these are arranged in pairs on the ventral side of the body, and united by nerve fibres into a ventral cord, which is connected in front with a nerve ring surrounding the gut and thickened above into cerebral ganglia. In many worms (e.g. tapeworms and flukes) the nervous system is of much simpler structure. The sub-kingdom of worms contains a very large number of forms. It is only necessary to mention here representatives of three classes: Segmented worms (Annelida), round worms (Nematelminthes), and flat worms (Platyelminthes).

CLASS: =ANNELIDA= (SEGMENTED WORMS).

Segmented worms with rounded (earthworm) or flattened (leech) bodies, and possessing both mouth and anus. They fall into two sub-classes: I. Leeches (Discophora), II. Bristle-worms (Chætopoda). The first possess suckers as organs assisting locomotion, the latter foot-stumps, which bear longer or shorter bristles; but these foot-stumps may be absent, and the bundles of bristles are then simply imbedded in pits. The latter is the case in the only members of the class which interest us here, i.e. the earthworms.

The =Earthworms= (Lumbricus).

There are several species in the genus, but all agree in their habits. The body of the earthworm is slender and cylindrical, tapering in front and somewhat flattened behind. On the ventral side of the second segment is found the opening of the mouth. There are no eyes, though these animals are sensitive to the action of light. The earthworm is hermaphrodite (p. 16); when two individuals pair they mutually fertilize each other. On a warm summer evening two adjacent worms creep half out or nearly out of their burrows, and apply the front parts of their bodies together, especially a reddish, swollen part found at about the middle of the anterior half of the body. In this region the glands in the skin are very strongly developed, and secrete a substance which surrounds the eggs as a capsule as they are being laid. Earthworms are chiefly found in damp humus, or, at any rate, not in very poor sandy soil or clay. From time to time they carry their burrows up to the surface in order to get rid of the undigested remains (“worm castings”) of the humus and vegetable matters which have been taken into the body. The burrows run down obliquely into the soil, or more rarely vertically, to the depth of eight feet or more; they end in an enlargement, where the worm remains coiled up during the winter, after having closed the mouth of the burrow with a plug of leaves, twigs, paper, straw, etc. Although the earthworm chiefly subsists on the organic matters found in earth rich in humus, it also devours the leaves of cabbage, onion, and other plants, and especially seedlings (particularly those of beet). It draws these parts of plants about four-fifths of an inch into its burrow, and moistens them there with an acid fluid it secretes, and which acts upon them before they are taken into the body. Earthworms may effect considerable damage by destroying seedlings, particularly in damp fields, though this damage is always local. A not inconsiderable amount of benefit is to be set against this. By means of the burrows which they dig earthworms cause air to penetrate into the soil much better than it could otherwise do, which is known to be of the greatest importance for plant life. Earthworms are extremely important owing to the large numbers in which they are present in the soil, and for another reason besides the one just given. Darwin shows that in many parts of England a weight of ten tons of earth per acre passes through the bodies of earthworms, and is brought to the surface by them, so that in a few years the entire humus-containing surface layer of earth has passed through their bodies. They therefore prepare the soil in an excellent manner for the growth of plants, by continually exposing it to the air. They cause stones to sink in the soil by throwing out at the top earth which naturally consists only of particles small enough to pass through their intestines. They play the part of gardeners by thoroughly mixing together the particles of soil, and bury under their castings, in a shorter time than one would imagine, objects found on the surface of the soil (bones, oyster-shells, dead animals, leaves). Plantfood is quickly formed again from these buried matters. Earthworms, therefore, play a very important part in the economy of nature; indeed, many regions, now occupied by luxuriant pastures or fertile cornfields, would be a waste, had it not been for them. Where, however, in damp spots they injure seedlings, they may be collected, either during the day after a warm rain, or in the evening, at which times they lie half out of their burrows. If a decoction of walnut leaves is poured into these, they will crawl out. Enemies: Mole, shrews, hedgehog, toads and frogs, ground beetles, rove beetles, mole-crickets, centipedes, etc.

CLASS: =NEMATELMINTHES= (ROUND WORMS).

Body cylindrical, unsegmented; body-wall tough, hooklets or spines may be present on it, but deeply imbedded bristles are always absent. The gut may be absent (some parasites), but this is exceptional. There are no special organs for circulation and respiration. Sexes distinct in the large majority. I will deal with only one of the orders belonging here.

ORDER: =Nematoda= (THREAD WORMS).

FIG. 128.—Diagrammatic transverse section through the body of a Thread Worm, internal organs being omitted: p, cuticle and skin; q, muscle layer; a, lateral lines; b, dorsal and ventral lines. ]

Elongated, thread-shaped or spindle-shaped, unsegmented. A gut, terminating in a ventral anus, is present. Outer investment of the skin smooth, often weakly ringed or striated. The muscle layer underlying the true skin is interrupted here and there, where the skin itself stretches further inwards. In this way are distinguished the lateral lines or fields (Fig. 128, a), which run right along the sides of the body, dividing it into a dorsal and a ventral region. There are often present as well two smaller but similar dorsal and ventral lines, respectively situated above and below (Fig. 128, b). Mouth usually surrounded by lip-like folds, but more or less distinct jaws may also be present. The anus either lies at the apex of the tapering posterior end of the body (trichina), or further forward, on the ventral surface. Among the Nematodes are included a number of relatively small species, living free in the earth, and sucking plant parts, while other forms fairly closely related live parasitically in plants, and often cause very serious plant diseases (e.g. Beet Eelworm); a larger number of species are parasitic in animals. The free forms and those parasitic in plants lay relatively few, but very large, eggs, although, in several species, increase is furthered by a succession of many generations in the year. The Nematodes parasitic in animals lay very numerous eggs, even several millions. Harmful species are known from the following families: 1. =Palisade Worms= (Strongylidæ), 2. =Whip Worms= (Trichotrachelidæ), 3. =Slender Thread Worms= (Filaridæ), 4. the =Round Worms= (Ascaridæ), 5. =Eelworms= (Anguillulidæ).

I will successively treat of the harmful forms, but since many species belonging to different families infest the digestive organs of the different domesticated animals, causing similar symptoms of disease which may be dealt with in much the same way, the following general sketch is first given:—

=Nematodes in the Gut= (more in young animals than old) cause the following symptoms: (1) Appetite variable. (2) Nutrition in general affected, even if sufficient food is taken; constipation or diarrhœa; belly much drawn in or else, and usually, swollen out. The animal itself is thin, and has (except horse) a tendency to vomit. (3) An itching all over the body, especially at the nostrils and anus. The animal rubs and bites the sides of its body. (4) Tongue covered with a thick, soft, yellowish coating. A sweet smell from the mouth. (5) The skin is tense, lacking its usual elasticity. (6) The animal suffers from spasmodic colic, and (7) disturbances of the nervous system (whining or crying; unrestrained or suppressed fits). Remedies: Horses and cows infested with thread worms may be given chopped carrots, beets, and turnips, previously mixed with sugar or crushed sugarcandy. Roasted oats are also good. For sheep finely crushed glass, kneaded into pills with bread, will always suffice. Gritty sand in the food may also be of use. Pigs should be given sour milk, acorns, unripe cheese, horseradish. For dogs, sausages containing garlic, as much flesh food as possible, strongly salted food, milk boiled with garlic. In all cases iron may be given. The advice of a veterinary surgeon should be sought in the matter of medicines (tansy, male fern root, tartar emetic, arsenious acid, etc.).

Family: =Strongylidæ= (Palisade Worms).

Spindle-shaped; anus on the tip of the hind end of the body; in all thread worms the rectum and male sexual organs open by a common cloacal opening, which, in the palisade worms, is surrounded by an umbrella, or cup-shaped apparatus (bursa), kept expanded by means of muscular ribs (Fig. 129).

Here belong—

The =Giant Palisade Worm=, or =Strongyle=, (Eustrongylus gigas). Female from a foot to thirty-nine inches long, and as much as two-fifths of an inch thick. Male six to sixteen inches long; reddish. Lives in the cavity (pelvis) of the kidneys in horses, oxen, dogs, and man; causes degeneration of the kidneys, with blood in the urine, nervous diseases, and disturbance of the feelings and intelligence.

FIG. 129.—Tail of male Strongylus armatus, strongly magnified. ]

The =Armed Palisade Worm=, or =Strongyle= (Strongylus armatus), four-fifths of an inch to two inches long, one twenty-fifth to one-twelfth of an inch thick; reddish brown. Taken into the gut of the horse with the drinking water as a young, minute worm, it bores through the walls of this organ into the blood-vessels branching there. Later on it bores into the walls of the larger arteries of the hinder part of the body, especially into those which carry blood to the wall of the gut (particularly anterior mesenteric artery). At those parts of the arterial walls where it collects in large numbers, swellings (aneurisms) are produced, varying from the size of a pea to that of a hen’s egg. A constriction is often developed quite close to this swelling, and a plug of fibrin may also be formed within the artery, so that the circulation in the wall of the gut is greatly hindered. As a result of this the glands and muscles in the wall of the digestive tube refuse their office, so that regular digestion and onward movement of the food do not take place. This leads to colic. As soon as the strongyloid larvæ have become adult, they pass from the walls of the arteries into their cavities, and are carried by the blood-stream to the walls of the gut, which they penetrate in order to reach its cavity, where (cæcum and large intestine) they pair, after which the female lays eggs, which are carried to the exterior in the dung. The quickly hatched young seek water, mud, or damp earth, where they live until, by some means (e.g. with the drinking water) they manage to enter the gut of a horse or (more often) ass. Preventive Measure: Horses and asses must not be allowed to drink stagnant water.

The =Stomach Palisade Worm=, or =Strongyle of the Sheep= (Strongylus contortus). Male one-half to two-thirds of an inch, female three-quarters to four-fifths of an inch long; whitish or reddish, somewhat coiled at both ends. The disease of the stomach, and diarrhœa, which affect lambs, usually in spring, and result from the presence of these worms in large numbers in the true or fourth stomach, lead to emaciation, weakness, and poverty of blood. Development unknown. Nutritious food will cure lambs which are not very badly infested, but hastens the death of those which are.

The =Lung Worm= of Lambs (Strongylus filaria). Male an inch, female as much as three and a half inches long, thread-shaped, white or yellowish. It appears that the young worms are taken into the stomach of a lamb (or sheep) with the drinking water; they are found there in May, June, and July. They quickly climb back into the throat, from which they get into the windpipe and its branches. There they penetrate the mucous membrane, where, until they have reached the sexual stage, they are found imbedded in small swellings, which they quit at the end of winter or the beginning of the next spring, if their host lives so long. The female bears living young, which as very minute worms may be met with by the hundred in the mucous lining the windpipe and its branches. A direct transference of the parasite from one sheep to another does not take place, since the young born in the mucus secreted by the walls of the air-tubes must first live and grow for some time in water or slime before they are able to undergo further development in the body of a sheep or lamb. The fate, however, of the young worms which pass to the exterior in the mucus is not yet sufficiently known. Symptoms of Disease: Running of slime from the nose, difficulty of breathing, cough, emaciation, poverty of blood. Death ensues in from two to four months. Recovery only of very strong individuals infested by comparatively few parasites, most of which they cough out. Preventive Measures: In regions where the evil is very prevalent the young sheep must not be allowed to go into the meadows. If it is impossible to keep them penned in, a little food and water may be given before sending them to pasture in the morning. In this way the danger of infection will be somewhat lessened, since it is then less likely that the animals will eagerly betake themselves to pools and ditches in order to quench their thirst. Since during the months May to July the young worms (most probably taken in with the water drunk) are found in the stomach, it is good during this time to give vermifuges to the lambs and sheep. For medicines a veterinary surgeon should be consulted.

The =Small-tailed Palisade Worm=, or =Strongyle= (Strongylus micrurus). Thread-shaped; male one and two-fifths, female two and two-fifths to two and four-fifths of an inch long; lives in oxen (especially calves) in swellings of the arteries, also in the windpipe and its branches. Severe bronchitis.

Family: =Trichotrachelidæ= (Whip Worms).

Small, slender, elongated worms, with the anus or, in the male, cloacal aperture at the hinder end of the body; the latter, however, is not—as in palisade worms—surrounded by an umbrella or cup-shaped expansion. Here belongs: