NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
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The Pedipalpi (Figs. 1 and 2).—These are composed of four joints, of which
the details of structure vary much in the different genera. In the Rhipicephalinæ
the whole pedipalp is very short, thick, and massive. In the Ixodinæ it is
longer and, as a rule, much simpler, in arrangement. (Figs. 1 and 2.)
In its simplest form, the pedipalp forms a somewhat leaf-shaped organ.
The different segments are but little differentiated, and carry only small spines.
In the palps of Rhipicephalus and Hæmaphysalis, the second and third joints
are much enlarged, and show considerable elaboration of structure. In Hæma-
physalis the second joint carries a sharp process characteristic of the genus.
The first joint in the Rhipicephalinæ is usually inconspicuous, and of simple
form, as, also, is the small fourth joint. The second joint is expanded in a
dorso-ventral direction, so that it forms with its fellow a distinct sheath to the
mouth parts. It usually carries, on its ventral surface, a row of conspicuous,
serrated spines, which meet in the middle line. The third joint is also swollen
and often carries dense processes of the chitin. Upon its ventral surface is an
area covered with membrane which bears the small papilliform fourth joint. The
fourth joint generally carries a terminal bunch of small spines.
The scutum (Fig. 3).—The scutum is a dense chitinous plate, covering
in the male the whole, and in the female, a portion, of the dorsum. Its shape
varies in different species. It may be emarginate or non-emarginate. It
may be furrowed or ornamented with punctures or coloured spots. Perforations
(eyes) may be present or absent. Eyes are present in Rhipicephalus,
Dermacentor, and Hyalomma, absent in Hæmaphysalis Hæmalastors, and
Ixodes.
On the dorsum behind the scutum there are present sometimes two
plates resembling the porose areas on the rostrum (Dorso-submedian porose
plates).
The anal opening (Fig. 3).—The anus is conspicuous. It is situated
about one-third of the body length from the posterior margin. The actual
opening is slit-like, guarded by two lateral semi-circular plates of chitin. It is
surrounded by various structures utilised in the identification of species, viz.,
the anal groove, anal plates and ventral plates.
The anal groove (Fig. 4).—A groove (the anal groove) may be present,
either anterior to, or posterior to, the anus. In Ixodes the groove lies anteri-
orly, and opens posteriorly. In Aponomma, Hyalomma, and Amblyomma, the
position is reversed.
The anal plates or clypei.—These are present in the males of certain
species. They are conspicuous plates of chitin, lying on the ventral surface
upon either side of the anus. Four plates two on each side, are present
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in the male of Rhipicephalus . The shape of the plates varies in different
species as, for instance, in the case of R. annulatus and R. decoloratus.
FIG. 3.
Dorsal and ventral views of a male tick (Hyalomma).
The ventral shields (Fig. 3).—These are, as a rule, less conspicuous
schlerites, which cover the ventral surface in the male. The arrangement of
the plates differs in the different species.
Marginal festoons.—Also most marked in the males of certain species,
FIG. 4.
Ventral view of Aponomma.
notably in Ambylomma, where they are eleven in number. The median festoon
in some males ( R. decoloratus, R. caudatus ), forms a short but distinct tail.
The genital opening.—Close behind the rostrum on the ventral surface is
the opening of the genital canal. It is smaller, and much less conspicuous, than
in the Argasidæ and in the gorged female is seen only as a minute pore (Pl. VI,
fig. 5).
2 2
The stigmata .—The stigmal plates, or Peritremes, into which the tracheal
system opens, lie behind the origin of the fourth pair of legs. Considerable
variation exists in the size and shape of these organs in the different species and
genera. They also differ in many cases in the two sexes. They may be cir-
cular, or oval, triangular, or comma-shaped as in the males of Hyalomma , where
they are comma-shaped with a long tail.
FIG. 5.
Coxae of first pair of legs.
A. Hhipicephalus.
B.
H y a l o m m a
.
The legs.—The legs consist of six podomeres. The basal joints (coxæ)
are enlarged and exhibit variations in different species. The first pair of coxæ
may show large and conspicuous teeth or may be bidentale (Fig. 5). The
fourth coxa in Hœmaphysalis carries a spine or tubercle. Tubercles may be
present on all the coxæ. The podomeres carry certain spines and hairs. The
terminal podomere (tarsus) may carry one or more "spurs" (Fig. 6) which are
of use in identification of species. The tarsus also carries two large curved
claws and a pulvillum.
FIG. 6.
A Tarsal joint with a single spur.
B. Tarsal joint with two spurs.
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The Argasidæ. —In the Argasidæ the head arises from the ventral surface,
and the animal is completely devoid of any scutum. The stigmata are situated
between the third and fourth legs (fifth and sixth appendages). The limbs, even
in fully-grown and gorged animals, are large and strong in proportion to the body.
The pulvillum of the tarsi are absent in the adult. The palpi are free,
short, filiform, and consist of 4 segments. The eyes are absent in Argas
and may be present or absent in Ornithodoros. There is a hood-like fold,
(the Camerostome) in Ornithodoros, lying in front of and around the base of the
head. This is not present in Argas. The abdomen does not become hypertro-
phied, as in most of the Ixodidæ, out of all proportion to the head and limbs, and
growth takes place uniformly, the fully developed animals being identical, in all
except size, with the smallest forms. The males are scarcely distinguishable
from the females.
A minute description of O. savignyi (Audouin) has been given by
Neumann. Of this the following is a translation :—
" Ornithodorus savignyi (Audouin).
" Body a short oval, rounded at the extremities, sometimes a little pinched in
laterally about the region of the origin of the third and fourth legs. Earthy
yellow when young, darker yellow or even blackish-brown in the adult state. The
terminal points of the legs lighter in colour. The body is covered with granu-
lations, which become larger as the animal increases in size. Hairs are abundant,
arising from between the tubercles. On the dorsal surface there is a median
prominence, limited behind by a transverse sulcus lying towards the posterior
extremity of the body. It is marked in the middle by a depression. Seven
similar depressions, one of which is situated at the anterior extremity of the
prominence, extend to a certain distance from the anterior edge of the body.
Each of these depressions becomes a deeper sulcus behind. The internal ones
abut upon the anterior part of the prominence, the two next upon the sides, the
two external ones limit laterally the transverse fold, which they join and deepen.
Another transverse sulcus is situated just in front of the posterior border of the
body. On the ventral surface, a transverse sulcus, concave posteriorly, is
situated immediately in front of the anus (pre-anal sulcus), and joins the supra-
coxal groove. Behind the pre-anal groove, on each side, are three symmetri-
cal longitudinal depressions, especially well marked in large specimens. The
middle grooves are long and incurved at either end. A short reversed γ-shaped
depression abuts upon the anus, the limbs lying between the internal and middle
sulci. The coxal fold is little marked ; the supra-coxal fold well marked.
The folds and grooves are limited behind by the pre-anal sulcus.
" The stigmata are placed behind and above the supra-coxal folds. They
are semi-lunar in shape, 600 μ in length. The anal area is broader than long,
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450 µ by 400 µ. Four eyes, two on each side, are situated upon the supra-
coxal fold, one above the bases of the front pair of legs, the other in the
interval between the 2nd and third pairs. They consist of a circular smooth
convex prominence 250 µ to 300 µ in diameter.
"The integument is thick, covered with granulations, measuring in the case
of large individuals 100 µ to 200 µ. They consist of irregular hemispherical
prominences, pointed at their summit, and thickened in the rest of their extent,
puckered and crenelated at their base. Between them narrow depressions form
a polygonal network. In the large sulci of the dorsal and ventral surfaces the
granulations are replaced by oval dimples 50 to 75 µ in diameter, each divided
into a large number of small contiguous polygonal areas.
"The rostrum powerful, more or less covered about its base in an infundi-
buliform camerostome. From the base of the palps to the extremity of the
gypostome, about 800 µ in large individuals. Cheliceres 2.4 mm. of which 200
µ is taken up by the digit and 900 by the shank, 1.3 mm. is occupied by the
base. The internal apophysis of the digit is in the form of a simple claw,
inserted a little behind the middle of the apophysis, external to the basal tooth.
The upper tooth is thickened and has a short point. There is no middle
apophysis apparent. The sheath is a little thickened in its anterior part, simply
striated in the rest of its extent. The hypostome is short, large at the base
rounded or pointed at its extremity. The teeth form three longitudinal parallel
series on the outer part of the hypostome, of 12 to 13 teeth each, of which the
external ones are the strongest. Internally, two or three more or less short
series, commencing only in the middle, or posterior third, of the base of the
hypostome end behind at the same level. They consist each of 5 to 8 small
teeth. There are two spines at the base of the hypostome. The palps measure
1.36 mm. 400, 400, 250, and 310 µ, from first to last joint, respectively. The
segments are cylindrical, of rapidly decreasing thickness from the first to the
fourth. Upon all sides of each segment there are some thick hairs of unequal
size having blunt points. Especially upon the first and not upon the last are
some blunt spines. The last segment is rounded at its extremity and is bare
without cirri.
"Legs strong, the fourth pair one and one-half times as long as the first.
Bases contiguous, decreasing in size from the first to the fourth pair. Striated
on the ventral surface. Granular on the dorsal and posterior aspects, with a
transversely ribbed pad at the distal extremity. The second segment broader
than long in the case of the first two pairs of legs, longer than broad in the others.
A little swollen with a distal pad. The third segment very thick at the distal
extremity. The fourth segment short in the first three legs, twice as long in the
fourth. The fifth segment carries on its dorsal surface, in the first three pairs,
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three successive teeth, the two proximal quadrangular, the distal conical. On
the fourth pair two conical teeth only. The tarsi carry on their dorsal surface
three proximal teeth, a basal one upon the proximal pseudo-segment of the
three last pairs, the other close to this. Both are quadrangular. The third is
conical and situated near the distal extremity. Thick and rough hairs and
small spines are present on all the segments, except on the bases."
In addition to the above minute description, it will be necessary to
draw attention only to certain points of special moment. Of the sulci, those of
greatest importance, and the only ones which are not obliterated when the animal
is fully gorged, are:
—
1. The supra-coxal sulcus. —This important sulcus, which gives rise to the
supra-coxal fold, and extends quite around the anterior portion of the body, is
distinguishable even in the larva. The supra-coxal fold itself is a conspicuous
structure. It has already been noted as carrying the eyes, which in O. savigny
var. caeca appear to be absent but which are readily made out in the Indian
species.
2. The pre-anal sulcus. —This is an extremely deep fissure, which forms a
landmark in sections.
3. The sulci about the head.— The conical head can be retracted to a consi-
derable extent into a fold of the integument (camerostome). At the junction
of the two is a deep groove, which is never quite obliterated, even when traction is
made upon the rostrum, and becomes much deeper when this organ is retracted.
Around the base of the camerostome is a second circular groove, which serves to
separate this fold from the coxa of the first pair of legs, the genital orifice, and
the supra-coxal fold. The latter part of the groove, that is, the portion lying
above the head, is somewhat shallow, and can be smoothed out by forcibly
flexing the head upon the body, as occurs in oviposition. When this is done,
a broad reversed V-shaped opening is disclosed, into which a stout hair
can, without much difficulty, be passed. During oviposition, a protuberant
mass, apparently the prolapsed duct of the cephalic gland, projects from this
spot.
On the coxæ of the first pair of legs, lying within the groove which separates
this from the coxa of the second pair, there is a pore, from which the secretion
of the large coxal gland, described later, is at times exuded.
The mouth parts. —The structure and function of the mouth parts have an
important bearing upon the question of disease transmission, and it will be most
advantageous to discuss them along with the internal anatomy of the tick.
The genital opening. —In both sexes this forms a large and prominent papilla,
surrounding a wide transverse fissure. In the male a short horny penis lies
within the genital canal, but is not visible externally.
E
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V.
THE INTERNAL STRUCTURE OF TICKS.
Technique. —Ticks are most conveniently examined by preliminary dissection
under normal saline, the separate organs being subsequently removed for the
purpose of examination in the fresh state, for the preparation of films, or for
sectioning. Sections of the whole animal may also be prepared, if certain
precautions are observed. The external covering of ticks is extremely resistant to
penetration by fluids, and if no opening be made, embedding can with difficulty
be carried out. Again, owing to the tension of the body contents, a large
incision, prior to hardening, will result in extrusion and considerable displacement of
the organs. A very small nick is therefore made in the chitin, at an unimportant
part, and the tick placed in alcohol for one hour. If, on further enlarging the
incision, the blood is found no longer fluid, slices from 1 to 2 mm. in thickness
are made in the required direction. If necessary, the tick may be replaced in
alcohol, until the requisite penetration, to allow of this procedure, has taken
place. The slices are embedded in paraffin in the usual way, care being taken
to use specially dehydrated alcohol, and as short periods in the different fluids as
possible. Under this treatment, Rhipicephalus cuts very readily. A difficulty
occurs in the case of Ornithodoros, owing to the very dense cheliceres and
apodemes of the head and it is necessary to use very sharp razors. In many
cases softening of the tissues in Eau de Javelle may be resorted to.
The sections are fixed upon slides by the hot water method, or by the
use of fixative. Obreggios method, though excellent for the study of the
relations of the chitinous parts, is not, as a rule, necessary and has several dis-
advantages.
Except for special reasons, it is undoubtedly preferable to remove the organs
separately. They may be fixed in perchloride, or in alcohol. They can be
embedded in an extremely short time, owing to their delicacy and ready pene-
trability.
In the examination for small parasitic forms, sections are by no means so
suitable as films or fresh preparations. Films are best made by means of the
edge of a microscope slide. If a delicate tissue has been already mounted as a
fresh preparation, it can always be converted into a dry film by forcibly sliding
off the cover glass.
For the dissection of ticks, a small glass trough, half filled with a mixture
of paraffin and lamp-black poured upon lead shavings, is most suitable. The
glass troughs used for staining a single slide are convenient, and can be placed,
if necessary, on stage of the microscope, or dissecting lens. A lens magnifying
fourth or five diameters is most helpful in observing the stages of dissection.
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To dissect a tick, it is taken lightly between the finger and thumb of the left
hand. With a sharp scissors, very fine tangential slices are snipped from the
sides. The dorsal and ventral surfaces, by this manœuvre, should be completely
separated except, in the case of the Ixodidæ, at the scutum.
At the first snip the distended diverticula will prolapse from the wound,
and will be somewhat injured in the subsequent cuts. If ordinary care be taken,
this will be found not to interfere at all with the later stages of dissection. Having
cut all round the tick, it is gently laved in normal saline to remove free blood, and
is placed in the dissecting dish. By using one pair of forceps to seize the ventral,
and another the dorsal flap at their posterior ends, the latter may be readily
dragged forward over the head, leaving all the viscera in situ attached to the
ventral surface. A few fine entomological pins, passed through the edge of the
chitin, will retain the tick in position during the subsequent operations. It
will be necessary to rock the dish and change the saline from time to time.
The larger specimens of Ornithodoros make excellent subjects for dissec-
tion. The chief anatomical features can be made out by merely displacing the
more massive organs, and by removing with a fine forceps the tissue, chiefly fine
tracheal and fat body lobules, which hold these in position.
Over the whole dorsum lies a fine membranous expansion of tracheæ
and trabeculæ of the fat body. Lying in this, in the median line, is the delicate
tubular heart. Posteriorly, at about the junction of the middle with the poste-
rior third of the body, this is considerably dilated. Stripping off the expan-
sion, the main mass of the viscera, consisting largely of the large dark red blood
sacs of the alimentary canal, are exposed. By carefully unravelling these,
the arrangement of long diverticula, described later, can be made out. Lying
upon the diverticula in the posterior portion of the body is the ovary, studded
with developing ova. Upon either side of the ovary, are the coiled oviducts,
and in the middle line is the large conspicuous bilobed spermatheca. In
almost every region of the body, a portion of the thin coiled malpighian
tubules will be found. Behind the spermatheca is an opaque white organ,
having very thin saccular walls, and filled with characteristic white secretion
from the malpighean tubules. This is the rectum, which in ticks serves as
an excretory bladder. By displacing the diverticula from the extreme
anterior portion of the body in Ornithodoros a bilobed glandular organ, the
cephalic gland, is displayed. Further back, the bulbous ends of the cheliceres
with radiating muscular fibres are seen. Around them will be noticed the
ring-like chitinous fold at the base of the rostrum. By displacing to one side
the whole of the anterior and lateral diverticula, a number of further structures
are apparent. Passing in from the stigmatic openings is a leash of tracheal
branches, of which the large anterior ventral trachea is the most conspicuous.
E 2
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Lying upon the origin of the first and second legs is the large racimose gland
which functions as the salivary gland in ticks. Lifting this gland by its poste-
rior extremity, which lies on the anterior ventral trachea, and tracing it
forward, the short salivary duct will be apparent entering the ring-like fold of
chitin, already mentioned, immediately beneath the cheliceres. Lying partly
under the salivary gland, and partly internal to this structure is a large saccular
organ, the coxal gland, conspicuous from the number of tracheæ which supply it.
By careful examination the delicate, colourless œsophagus can be made
out entering the lower surface of the large median blood sac of the alimentary
canal, whilst lying behind the spermatheca is the fine hair-like termination of
the sac in the rectum. To the rectum can be traced the attached end of the
two extremely long malpighian tubules. To display the œsophagus in its
passage from the pumping organ to the alimentary sac it is necessary to
tear away the dense mass of muscle from which it will be seen to emerge.
By seizing the muscular mass boldly in the forceps, the unattached ento-
sternum surrounded with muscle will come away, exposing the central ganglion,
perforated by the œsophagus. By seizing the bulbous ends of the cheliceres
they may be drawn from their sheaths. Lying beneath them is the horizontal,
entoschlerite of the head. Beneath this, again, is a dense mass of muscle
within which lies the chitinous pumping pharynx.
In the male, in the position of the ovary in the female there is a delicate
tube abundantly supplied with tracheæ. On either side this is continuous with a
coiled duct much resembling the oviduct in the female. In the middle line,
much in the position of the spermatheca in the female, is a curious lobular
organ, the white gland.
In Rhipicephalus and Hyalomma the general relations of the organs are
similar to that already described in Ornithodoros. The only structures whose
nature may not be at first clear in dissections are the long branched cephalic
glands, and certain small dermal glands which lie in the fat body.
The following is a detailed description of the organs and tissues of ticks:—
ORNITHODOROS.
The alimentary canal. —Into the floor of the mouth opens a chitinous
pharyngeal pump. This leads to a narrow and straight œsophagus, which, after
perforating the central ganglion, enters the enormous saccular portion, which
with its diverticula forms the great bulk of the body contents. Posteriorly an
extremely fine canal, which appears to be a functionless rudiment, joins the
central saccular gut with the rectum. Opening into the mouth are the ducts
of glands, which function as salivary glands, though they are probably not
homologous with the salivary glands of Scorpio. Opening into the rectum on