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).
[Illustration:
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).