NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
4 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, I
Nervous system. The nervous system consists of two large ganglia situated on
the dorsal side of the œsophagus and connected by a transverse band of nerve
fibres. From each of these ganglia three nerves pass anteriorly and three posteriorly.
Close to the ventral sucker and in the posterior part of the body, the nerves on
either side are connected together by the commissures.
Excretory system. The excretory system consists of an excretory bladder,
opening at the posterior end, either terminally or subterminally. This may be
simple, elongated or sac-like, or it may assume different shapes : being S-shaped
as in Opisthorchis, T-shaped as in Eurytrema or Y-shaped as in Echinostomidæ and
some other forms. The bladder may give out a few or more branches which divide
and subdivide into smaller and smaller capillaries, which ultimately terminate
blindly in conical cells having a bunch of cilia projecting into their cavities. On
account of the peculiar flickering movements of the cilia and their resemblance to
a flame, these cells are called the flame cells.
Lymphatic system. In the family Paramphistomidæ a system of one to three
pairs of lymph canals is present. These are usually branched, but occasionally they
may be without any branches. The members of this family have a thick body and
the necessity of a lymphatic system is, therefore, obvious.
Reproductive system.
Genital pore. The genital pore is situated in the middle line, on the ventral
surface, usually nearer the anterior end. Usually it lies level with the ventral
surface, but occasionally it is situated on a distinct genital papilla. In some species
of Opisthorchis it may be occasionally raised on a pedicel along with the ventral
sucker. Among the forms having the ventral pouch the male and the female genital
ducts open on a genital papilla situated in the pouch, on its dorsal surface. In the
genus Cotylophoron the genital aperture is surrounded by a sucker called the genital
sucker.
All the trematodes, with the exception of the members of the family Schisto¬
somidæ, are hermaphrodite.
Male genitalia. The male genitalia usually consists of two testes, but this
number may vary from 3 to 60 in the family Schistosomidæ. They usually lie in the
posterior part of the body, but occasionally one or more of them may be found in
the anterior half. They may be elongated, round, oval or irregular in shape and
their outline may be entire, lobed or branched. They may be situated symetric¬
ally one behind the other, obliquely one behind the other, dorso-ventrally or
obliquely dorso-ventrally.
HELMINTH PARASITES AFFECTING DOMESTIC ANIMALS
5
From each testis originates a fine duct, the vas efferens. Sooner or later the
vasa efferentia unite to form a common duct, the vas deferens, which usually enters
a sac, the cirrus sac. This organ may be absent in Opisthorchidæ and in some
Paramphistomidæ. Among the members of the latter family, the absence of a cirrus
sac is accompanied by the presence of a pars musculosa. The cirrus sac is situated
on the dorsal side and opens to the exterior by a genital pore.
The portion of the vas deferens enclosed in the cirrus sac is differentiated into
a vesicula seminalis, a pars prostatica and the terminal muscular portion, the
cirrus. The vesicula seminalis is usually a swollen, sac-like portion which may be
divided into two parts, one of which is coiled and the other sac-like. Following the
vesicula seminalis is a small portion of the vas deferens, the pars prostatica, into
which the unicellular prostatic glands open. The terminal portion of the vas
deferens is the thick muscular organ called the cirrus which is capable of being
protruded out of the cirrus sac and act as an organ of copulation. Occasionally
the cirrus may have fine spines on it.
Female genitalia. The female genitalia consists of an ovary situated near the
middle line, sometimes to the right side and sometimes to the left. It may be
either anterior or posterior to the testes. It may be round, oval or kidney-
shaped as in Pseudamphistomum. Its outline may be entire or lobed or it may be
a branched structure as in the genus Fasciola.
From the ovary a short oviduct proceeds towards the centre where it is joined
by the excretory ducts of the vitelline glands. These are grape-like glands, lying
on each side of the body and extending to a variable extent. They may extend
ventrally and dorsally and occasionally meet in the middle line in the posterior
part of the body. Each gland is composed of a varying number of smaller or
larger groups containing small acini. The function of these glands is to secrete
yolk material which is deposited over the eggs. From each group of vitelline
glands a small duct is given off. Many such ducts unite to form large anterior
and posterior ducts. These meet together and form a transverse duct. The
transverse ducts of each side unite in the centre of the body, slightly posterior
to the ovary and pour their contents into the oviduct. Occasionally a yolk
sac of varying size is noticed at the junction of the two transverse vitelline
ducts. Near the point of union of the common vitelline duct with the oviduct
a small thin Laurer's canal opens, which begins on the dorsal surface. Very
occasionally Laurer's canal has no external opening. On the inner side
of Laurer's canal, near its opening into the oviduct, is found a small sac filled
with sperms, which is called the receptaculum seminis. Occasionally the
receptaculum seminis may be absent. At the point of the union of the oviduct
6 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, I
with the vitelline duct and Laurer's canal or very close to it are numerous, radially
disposed, unicellular glands, the shell-glands which pour their secretion into the
dilated portion of the oviduct. In this dilated portion of the oviduct, the ootype,
the ova are fertilized and the yolk cells and the shell material is deposited over
them. The fertilized ova pass into the uterus which is the direct continuation of
the oviduct. It is usually coiled, but occasionally it may be straight. The uterine
coils are either confined to the central field of the body, disposed transversely or
irregularly or they may first pass posteriorly and then turn anteriorly. The
terminal portion of the uterus, occasionally differentiated into a muscular vagina,
passes by the side of the cirrus sac or the open vesicula seminalis, whenever the
former is absent, and opens to the exterior by the side of the male genital pore.
Usually both the male and female ducts open into a common genital atrium which
in its turn communicates with the exterior by the genital pore.
Eggs. The eggs are usually oval, but in Schistosomidæ they are sometimes
elliptical. They are yellowish brown or deep brown in colour. At one of their
poles there is usually an operculum, through which the embro escapes after it is
fully developed. The eggs of the genus Schistosoma have a terminal or lateral
spine.
Development. Among the trematodes both cross and auto-copulation is
known. The terminal portion of the uterus, known as the metraterm is used for
copulation. After copulation the spermatozoa travel up the entire length of the
uterus and are stored up in the receptaculum seminis. After fertilization which
takes place in the ootype, the segmentation begins and in some cases the embryo
is tully formed while the egg is still in the body of the parent. The digenetic
trematodes have alternation of generations (Metagenesis) as well as an alternation of
hosts. The adults are usually parasite of vertebrates and intermediate hosts are
molluscs. Occasionally in addition to the molluscan intermediate host there
is a second intermediate host, frequently an arthropod or a lower vertebrate.
Sometime after the eggs are laid, the larvæ are formed if their development
has not been already completed in the body of the parent. When the eggs come
in contact with water, the larvæ escape into it by opening the operculum or by
splitting up of the shell whenever the former is absent. The larva escaping from
the egg is called the miracidium. It is mere or less triangular in shape, with a
ciliated epithelium covering the whole body and a stilet at the anterior end. It
has a simple, sac-like gut with the secretory glands opening into it, the eye spots,
the nerve ganglia, a pair of excretory tabules with flame cells and a group of
germinal cells and the perthenogenetic ova. The miracidium swims in water by
means of its cilia and as soon as it comes in contact with a mollusc of an appro-
HELMINTH PARASITES AFFECTING DOMESTIC ANIMALS
7
priate species, it makes its way into its body. It soon enters its lymphatic system
and is carried to its apical portion, the liver. In the meanwhile it loses its cilia
and all other organs and is transformed into a sac-like body known as the sporocyst
which contains only the germ cells. These latter may give rise to other sporocysts,
but usually they give rise to the second generation known as the redia. These
have a pharynx, a sac-like gut, an excretory system and the germ cells. Some
redia have, in addition, a birth pore and a pair of appendages in the posterior half.
The redia inside the sporocysts, usually more than hundred, grow larger in size
and rupture the wall of the sporocyst and lie freely in the lymphatic fluid of the
mollusc. Here they develop rapidly and give rise again to redia or usually to the
larvæ of the third generation, the cercaria. These may vary in structure in diffe-
rent species, but usually they have a long tail which may be simple or bifid. The
rest of their anatomy resembles very much that of the adults excepting the geni-
talia, which are still undeveloped. The cercaria, when mature, escape from their
mother sporocysts or redia, by either rupture of the wall or through the birth
opening, if the latter is present. By their active movements they make their way
through the tissues of the molluscan host and come to lie between its shell and the
mantle covering. From here they escape into the water from time to time and
swim about actively in it. The cercaria of the blood-flukes actively penetrate the
skin of their final hosts and thus reach their destination, but in all other cases
they are passively transferred to them either through the second intermediate
hosts or through food or drinking water. The cercaria affecting the herbivorous
animals are encysted and deposited on vegetable matter, and the infection is
acquired when the latter is taken in by the animal. After their arrival in the ali-
mentary canal of an appropriate host, the cyst capsule is dissolved by the digestive
juices and the adolescaria or miniature adults emerge and migrate to their favourite
place of residence.
CESTODA.
Cestodes, popularly known as tapeworms, are parasites also belonging to the
phylum PLATYHELMINTHES. With the exception of Stilesia hepatica, which
occurs in the liver and the bile-ducts of sheep and goats, all the adult cestodes inhabit
the intestines of their hosts. The larval forms are, however, found in other loca-
tions, such as lung, liver, brain, muscles, eye, body-cavity, etc.
The body of a Cestode is usually distinguishable into three regions : the head
or scolex, the neck and the body proper or the strobila.
Scolex. This is the anterior-most portion of cestodes and bears the organs
of fixation. Except in Ligula it is a fairly conspicuous portion of the body. In
8 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, I
Fimbriaria a true scolex is not present, but it is replaced by a pseudoscolex. Occa-
sionally, e.g., in Stilesia globipunctata, it is deeply buried in the mucousa of the
gut and produces a button-like nodule.
Organs of fixation. In the order Cyclophyllidea the scolex bears four muscular,
cup-shaped suckers which, in some cases, e.g., in Rallietina echinobothrida, are
covered with spines. In addition to the suckers, hooks of varying shape and size
may be present. In Tænidæ a crown of smaller hooks alternates with that of
larger ones. The hooks are usually borne on a retractile structure called the
rostellum which is situated at the anterior end of the scolex. In some cases, e.g.,
in Anoplocephalidæ and Mesocestoididæ, the rostellum is altogether lacking and
in such cases the scolex is without any hooks or spines.
In the order Tetraphyllidea the scolex bears four ear-like lappets or bothridia
which may bear on them accessory suckers, or they may be divided into areolae
by transverse and longitudinal septa. In Ichthiotaenidæ a fifth sucker may be
developed in addition.
In Pseudophyllidea the scolex bears two longitudinal, shallow, sucking grooves
called the bothria. In Diphyllobothridæ the margins of a bothrium fuse to form
a tube. The bothria may occasionally be replaced by a terminal sucker.
Neck. In some cases, e.g., in Avitellina, there is an unsegmented region behind
the scolex, which is called the neck.
Strobila. This term is applied to the general body of a cestode consisting of
segments or proglottides.
In Fimbriarinæ external segmentation is obscured by secondary divisions of
folds, and in Ligulinæ it may be very rudimentary.
Proglottides. Great variations are noticed in the size and shape of proglot-
tides, not only in the different forms but even in the different regions of the same
individual. They may be longer than broad and sometimes broader than long.
They may be arranged one after the other in succession or a portion of the posterior
margin of a proglottis may overlap the anterior margin of the succeeding one.
Occasionally between the successive proglottides are seen interproglottidal glands
which may be arranged in a line or be diffuse. It is conventional to consider the
side on which the ovary is situated as the ventral one.
Cuticle. The body of a cestode is covered externally by a cuticle which may
occasionally bear spines.
Musculature. Three kinds of muscles are found among the cestodes. The
outermost layer consists of longitudinal muscle fibres, and internal to this there
HELMINTH PARASITES AFFECTING DOMESTIC ANIMALS
9
is a layer of circular muscle fibres. Besides these two kinds of muscles there are
also transverse or dorso-ventral muscle fibres.
Parenchyma. This is the connective tissue which, as in trematodes, fills up
the major portion of the body of cestodes. It is divided by the circular muscle
fibres into medullary or central and cortical or outer portions. All the essential
genital organs are usually situated in the medullary parenchyma while the nerves,
excretory canals, longitudinal muscles and the terminal portions of the genital
ducts are situated in the cortical portion. Certain cells of the cortical parenchyma
have in them concretions of carbonate of lime, which are called the calcareous
corpuscles.
An alimentary canal and cilia, except in the onchosphere of Pseudophyllidea,
are completely wanting in cestodes.
Nervous system. The nervous system of cestodes consists of the ganglia situat-
ed in the scolex, from which nerves are given off to the suckers, and longitudinal
nerves passing posteriorly throughout the entire length of the body, externally
to the muscular layers. The latter are connected with each other by numerous
transverse commissures.
Excretory system. The excretory system consists of a pair of excretory canals
on each side of the body. One of the excretory canals on each side is situated
dorsally and the other ventrally. All the four canals open into a vesicle situated
in the last proglottis. When the latter is shed, the excretory canals open directly
outside. In some cases the dorsal pair may be lacking or may be present only
in the anterior portion of the body as in Avitellina. The excretory canals give out
many side branches which divide into capillaries ending in the characteristic
flame-cells.
Reproductive system. All the tapeworms of the domesticated animals are
hermophroditic and each mature proglottis contains a complete set of male as well
as female genitalia. Usually the male genital organs develop before the female
ones. The proglottides in which the genitalia are not developed or partially deve-
loped are called immature proglottides; those in which they are fully developed
and are functional are called mature proglottides and those in which the uterus is
filled with fertilised eggs are called ripe or gravid proglottides.
In the large majority of cestodes a single set of male and female genital organs
is present; but in some genera, e.g., Dipylidium, Moniezia, Cotugnia, etc., double
sets of genitalia are found.
Genital pores. The external opening of the vas deferens is the male genital
opening and that of the vagina is the female genital opening. Usually the male
10 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ II, I
and the female genital openings open close together in a common genital atrium
which in turn opens to the exterior. In the order Pseudophyllidea the male and
the female pores are far apart. In Cyclophyllidea and Tetraphyllidea the uterus
is a closed sac, but in Pseudephyllidea it possesses a distinct opening to the ex-
terior. With the exception of Mesocestoides in which, like Pseudpohyllidea, there
is a ventral genital opening, the genital pore in Cyclophyllidea and Tetraphyllidea
is situated on the lateral margin of a proglottis. In these two orders all the pro-
glottides may have genital pores opening on the same side as in Hymenolepsis,
when they are described as unilateral, or they may be regularly alternating, in
which case the consecutive segments have these opening on the opposite sides in a
regular manner. In the species of the genus Tænia they open on one side of the
proglottis margin or the other in an irregular manner and for this reason they are
described as irregularly alternating. They may open in the centre of the proglottis
margin or anterior or posterior to it.
Male genitalia. These consist of the testes which are rounded bodies, situated
on the dorsal side, usually in the medullary portion. In the family Anoplocepha¬
lidæ they may lie even outside the excretory canals. Their number is very
variable : in the genus Diorchis they are only two, in Hymenolepsis they are three,
but in the species of Tænia their number may be as large as 500.
From each testis a minute duct called the vas efferens is given off. The vasa
efferentia unite together to form a vas deferens, which usually runs towards the
proglottis margin in a zigzag manner. Its terminal portion is capable of eversion
to a more or less degree and is called the cirrus. Occasionally the cirrus may have
spines on its surface. The cirrus is enclosed in a muscular sac called the cirrus
sac. This is usually small, but occasionally, as in some species of Hymenolepsis,
it may be a very prominent structure. In some cases the vas deferens may have
one or more dilations on it, each one of which is called the vesicula seminalis. The
cirrus sac is usually situated anterior to the terminal portion of the vagina, but
the order may occasionally be reversed. It may also be situated dorsal or ventral
to the terminal portion of the vagina.
Female genitalia. These consist of an ovary, which is usually a bilobed struc-
ture united by a transverse isthmus and situated in the centre of a proglottis. In
some genera, e.g., Avitellina and Stilesia, it is more or less globular and is situated
asymmetrically on the poral side of a segment. In the genera with two sets of
genitalia in each proglottis the ovaries are not central, but nearer the lateral
margins. Proceeding from the ovary is a short duct, the oviduct. The ova dis-
charged from the ovary pass into it and are fertilized in its proximal portion which
is called the ootype. In this portion also open the ducts from the vitelline and shell
HELMINTH PARASITES AFFECTING DOMESTIC ANIMALS
11
gland wherever these are present. The distal portion of the oviduct divides into
two branches, one of which continues as the uterus and the other as the vagina.
This latter is a curved duct running from the isthmus of the ovary towards the
genital pore. Near the ovarian isthmus it has a small dilatation, which is called
the receptaculum seminis, for the storage of the sperms. The distal end of the
vagina may occasionally be slightly swollen when it is called the vulva. In Diplo¬
posthe there are two vaginae in each segment. In Aporina the vaginal pore is
altogether lacking.
In regard to the arrangement and disposition of the vitellaria, there exists a
great diversity. In Cyclophyllidea they form a compact gland, lying posterior to
the ovary in the centre of the proglottis. They are double in the forms having a
double set of genitalia. In the genera Avitellina and Stilesia they are absent. In
Tetraphyllidea they are present in two lateral rows or in two broad dorsal and
ventral layers. In the order Pseudophyllidea they are scattered in the cortical
parenchyma.
The shell gland is usually situated posterior to the ovary. The function of
this gland is not known with certainty. The earlier helminthologists regarded it
to be concerned with the formation of the shell of the ova.
A great diversity exists in regard to the structure and disposition of the uterus.
It may be a central tube with horizontal branches as in the genus Tænia, a hori-
zontal sac as in Hymenolopis, a reticulate structure as in Dipylidium or like a horse-
shoe as in Paronia. It may be replaced by parenchymatous capsules as in Dava¬
ineidæ. In the genera Avitellina and Stilesia it is replaced by a fibrous capsule,
the paruterine organ. In Pseudophyllidea it consists of a convoluted tube which in
some cases assumes the form of a rosette. In Cyclophyllidea the uterus has no
external opening, the ova escaping from it by the disintegration and rupture of the
parenchymatous tissue. The genitalia in this order atrophy as the uterus develops.
In Pseudophyllidea the uterus has an external opening and the genital organs do
not atrophy even after its complete development.
Copulation. The protrusible cirrus transmits the spermatozoa to the vagina,
which are stored up in the receptaculum seminis. In Aporina, where the vaginal
pore is absent, the cirrus has to penetrate the tissues of a segment during copulation.
The actual fertilization takes place in the ootype. The ova of one proglottis may
be fertilized by the spermatozoa of the same or another proglottis or of a different
individual altogether, if several individuals are present in the same host. The
ovum after fertilization receives the secretions of the vitelline and shell glands,
wherever they are present, and is enclosed by a shell. Development begins imme-
diately and before the egg is deposited a hexacanth embryo is already formed in it.