NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
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Even during the day, but especially after dark, the ticks feed readily on
monkeys. Major Donovan, I.M.S., informs me that they feed with great readi-
ness on the human subject if merely placed upon the skin. Specimens fed upon
monkeys become fully gorged within fifteen minutes. If removed during the
process, they offer but little resistance and, indeed, often fall off at a touch.
After a full meal most of the sulci, except the more important ones, are
obliterated and there is a marked bulging of the ventral surface between the
origin of the legs. The head is retracted, and the legs are applied to the body,
whilst the animal evinces a tendency, if not disturbed, to lie without movement in
the earth upon which it has fallen. A curious feature in regard to the act of
feeding was first noticed by Donovan, when feeding some of the ticks in his
wards. As the tick distends, fluid is seen to accumulate between the ventral
surface and the skin of the host. At first this was thought to be serum
which had been voided by the tick. Further investigation makes it probable that,
in the main at least, the fluid is not serum, but the secretion of the large coxal
glands described later. When handling the larger specimens, one occasionally
sees a drop of perfectly clear fluid well up from between the coxæ of the first two
pairs of legs. This secretion is very abundant, and several large drops may form
in quick succession. Specimens in an unfed condition rarely exhibit this pheno-
menon, but it is readily observed if the tick is allowed to feed. The fluid is
alkaline to litmus, and has a marked effect in preventing the coagulation of blood.
After complete engorgement the animal drops to the ground and, being wet with
secretion, becomes so covered with adherent particles of soil that it may readily
be overlooked. The local effect of the puncture in monkeys is considerable, and,
as the tick distends, a zone of ecchymosis is seen extending around the puncture.
This area often reaches the size of a shilling or more.
The appearance of extreme rotundity, which is seen immediately after feeding,
is lost even in a few days, but the ticks remain distended for several weeks or
more. During this time the body gradually regains its flat and sulcate
appearance. A short time after feeding the animal casts its skin. After
moulting, the ticks are very active and run about as if searching for their
prey. The habit of raising the first pair of legs in the air is particularly noticeable
at this time. After moulting the ticks feed readily.
Fecundation occurs at various times, and it is not uncommon to find large
and fully-grown females, which already contained abundant spermatozoa in the
oviducts and spermatheca, in the act of coitus with males. Not only do the
males fertilise several females, but females undoubtedly receive sperm sacs
from more than one male. During copulation the male, which is usually
smaller than the female, hangs ventral surface upwards beneath the female by
means of all four legs, which are hooked over the lateral margin of the body of
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the latter. The legs of the male are arranged alternately with those of the
female, the first pair of the male lying internal to the first pairs of the female.
The act is completed by the passage of a large sperm sac into the genital
orifice of the female. I have never observed the proboscis of the male within
the vulva of the female.
In the main the act of oviposition is carried out similarly in the Argasidæ
and Ixodidæ. The female, prior to laying ova, becomes torpid and remains without
moving at one spot. Ova are then passed out and remain beneath the body. The
whole process takes a week or more. When a female is examined during ovipo-
sition, it is seen that the head is forcibly flexed on the body, so that the two
pedipalps lie on each side of the genital opening, which at this time gapes
widely. Above the head is a curious protuberant mass, not seen in the female
at other times. It appears to be the prolapsed duct of the cephalic gland, a
structure described later. From the appearance of this body it would seem
to serve some very definite purpose during oviposition.
The ova of O. savignyi are comparatively few, numbering hundreds in
place of thousands as in the cattle ticks. Each ovum is of large size, about
one millimetre in diameter. They are globular or very slightly oval, and of a
shiny black colour. In captivity they are often scattered over the surface of the
gravel, but normally they are laid in a loosely adherent mass, which lies beneath
the body of the female. The larvæ hatch very quickly, often in less than a week,
and the change to the nymph occurs before another week has elapsed. On
hatching, the larvæ are black in colour and globular in shape. The rostrum and
the three pairs of short legs are soft and imperfectly developed. The larvæ
lie quiescent, often upon their backs, and make no attempt whatever to crawl
or to seek food. After three or four days the larval skin is cast, and the
octopod nymph escapes. From the first the nymphs are very active, and at
once proceed to bury themselves in the sand. They are broad and flat, of a
light brown colour, and resemble exactly, in all except size and the absence
of a genital opening, the adult tick. They remain alive and active for many
weeks without food and exhibit great excitement when the gravel in which they
lie is breathed upon or disturbed. They feed readily.
Salmon and Stiles 28 describe the larvæ and nymphs of Argas miniatus
and Ornithodoros megnini. In A. miniatus the larva has long and well developed
legs with fully formed mouth parts. They are found feeding on the chicken.
In O. megnini the larva has a very large capitellum and long legs. During the
change from the larva to the nymph a quiescent stage (pupa-like stage) supervenes.
The nymph differs markedly from the adult in appearance, being covered with
spines which are not present in the mature tick.
The larval and nymphal stages of the Argasidæ therefore present great
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differences in the case of different species and the working out of the details of
these stages in O. moubata Murray and O. savignyi var. caeca (Neumann)
is required.* Since in O. savignyi (Audouin), the larva does not suck blood,
and indeed appears quite incapable of doing so, the transmission of disease by
this species can take place only after the first moult, and by the agency of
the nymph.
In the Ixodidæ two changes only of the skin take place, namely, at the
larval and nymphal ecdysis. In Ornithodoros changes of the skin are many,
and occur as the increased growth of the tick demands. In the process of
moulting the legs and the rostrum are visible beneath the outer skin, before
any rupture of this occurs. Eventually the cuticle is ruptured anteriorly, and
separates as a dorsal and ventral sheet.
It has been stated by some observers, that in ticks, a quantity of blood is
included in the shell of the ovum to act as reserve material. I have been
unable to obtain any evidence that this is so, and, as neither in the ova of
Ornithodoros nor in those of Rhipicephalus is blood to be detected, it is probable
that an error has in some way crept in. (Sect. VI, p. 48.)
* NOTE.—Since the above was written, Dutton and Todd have described the larva of O. moubata which
is inactive.
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III.
GENERAL ZOOLOGICAL CHARACTERS OF TICKS.
THE Arachnoidea, in which class ticks naturally fall, differ from the Insecta,
among other important points, in the absence of antennæ, and in the posses-
sion of four, instead of three, pairs of walking legs. The Arachnoidea include,
besides certain marine forms, mainly extinct, a large number of terrestrial species
of the following orders: Scorpiones (scorpions) ; Pedipalpi (scorpion-spiders, whip
scorpions) ; Araneæ (spiders) ; Solifugaæ (Galeodes, Pseudoscorpiones (book-
scorpions) Opiliones (harvest-men) ; Acarinæ (mites and ticks) ; the
Tardigrada (water bears) ; and the pentastomidæ.
Typical arachnids possess six pairs of appendages, the first or cheliceres, the
second or pedipalpi and the third to the six which form the four pairs of walking
legs. The first pair in ticks are converted into piercing mandibles, the second
function as labial palps, whilst the four pairs of legs are the third to sixth append-
ages respectively. In this order also the second pair of appendages (pedipalps)
are united at their bases behind the mouth, whilst the third, fourth, fifth and sixth
pairs are widely separated.
The most recent classification of the order is that given by Lankester, 21 who
recognises seven sub-orders as follows:—
Sub-order a. Notostigmata.
Possess 10 segments, the anterior four furnished with a single pair of
dorsally-placed spiracles.
It contains the form Opilioacarus.
Sub-order b. Cryptostigmata.
The integument is hard. A dorsal and ventral chitinous schlerite is
present. The tracheal openings are by stigmata in the articular
sockets of the last four appendages.
It contains the family : Oribatidæ.
Sub-order c. Metastigmata.
Integument hard. Tracheae opening by a single pair of spiracles above
and behind the base of the fourth, fifth, or sixth pair of appendages.
Gamasidæ,
It contains the families Argasidæ,
Ixodidæ.
Sub-order a. Prostigmata.
Integument soft. Tracheae, except in the aquatic forms where they
are atrophied, open into a pair of stigmata close to or above the base
of the chelicera.
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Trombidiidæ,
The order contains the families
Hydrachnidæ,
Halacaridæ,
Bdellicdæ.
Some of the Trombidiidæ (harvest-mites), attack man, and others are well
known objects, notably the scarlet plush species so commonly seen in the tropics
after rain. The Hydrachnidæ are water-mites. During their larval stages they
may be attached to various aquatic animals. Dye 22 has noted three species
attached to adult mosquitoes in Madagascar ( Anopheles, Mansonia and Culex).
The Halacaridæ are marine forms.
Sub-order e. Astigmata.
Minute species without tracheæ.
Tyroglyphidæ, cheese-mites, etc.
The order contains the families
Sarcoptidæ, Itch-mites.
Sub-order f. Vermiformia.
The order contains the family : Demodicidæ.
Sub-order g. Tetrapoda.
The order contains the family : Eriophidæ, or water-bears.
The sub-order Metastigmata includes nearly all the tracheate forms parasi-
tic on terrestrial vertebrates, and is practically synonymous with the term "tick."
The Gamasidæ are small forms found very commonly on beetles, but by no
means confined to this order. They have free, filiform palpi and chelate
mandibles.
The distinction between the Ixodidæ and the Argasidæ is based upon
the presence, or absence, of a dorsal schlerite or scutum. There are also other
and considerable differences between the two families, which are detailed later.
The Ixodidæ are sub-divided by Neumann23 into the Rhipicephalinæ and
the Ixodinæ, the former division containing the genera Rhipicephalus, Hæmal-
physalis and Dermacentor, whilst the latter includes the genera Ixodes, Hæma-
astor, Hyalomma, Amblyomma and Aponoma.
The following are the chief characters of the genera mentioned, as given by
Salmon and Stiles :
Rhipicephalinæ. Palpi not longer than broad, rostrum short. Anterior
portion of body emarginate.
Rhipicephalus.—Eyes present. Base of rostrum hexagonal (dorsally),
forming on each side a projecting angle. Palpi short and broad (Fig. 1). Stig-
mata comma-shaped. Two pairs of clypei in the male. The first coxa with two
large teeth (Fig. 5A).
Hæmaphysalis.—Eyes absent. Base of rostrum rectangular, twice as
long as broad. Palpi conical. The second segment of the palps has a well
FIG. I.
Rostrum of a Rhipicephalus.
FIG. 2.
Rostrum of Hyalomma.
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marked lateral conical projection. Stigmata comma-shaped or circular. Anal
shields absent in the male. The first coxa not bifid. The fourth coxa in the
male has a well-marked spur.
Dermacentor.—Eyes present. Base of rostrum broader than long. Palpi
short and thick. Stigmata comma-shaped. Anal shields absent in the males
The first coxa bidentate in the male and female. Scutum ornamented.
Ixodinœ. Palpi longer than broad, rostrum long. Anterior portion of
body straight or emarginate.
Ixodes. —Eyes absent. Palpi long. Anal groove surrounds anus anteriorly
and opens posteriorly. Scutum in the male does not cover the body laterally
and posteriorly. Stigmata oval in the male, circular in the female. Male
ventrally covered with six shields. Tarsi without terminal spurs. The female
has, dorsally, three longitudinal grooves on the abdomen, ventrally, two bell-
shaped grooves, the first having its apex at the vulva, the second at the anus.
Hœmalastor.—Eyes absent. Rostrum long. Palpi piriform in the male,
claviform in the female. Anal groove as in Ixodes . Stigmata circular in both
sexes. Legs very long. Dorsal and ventral chitinous thickenings in the male,
fine grooves in the female.
Aponomma. —Eyes absent. Anal groove s urrounds anus posteriorly and
opens anteriorly (Fig. 4). Anal plates absent. Base of rostrum pentagonal.
Scutum covers the dorsum entirely ; usually marked, with green spots ; in the
female shorter than broad. Stigmata comma-shaped.
Amblyomma .—Eyes present and conspicuous. Anal groove as in Aponomma .
Anal plates absent. Rostrum long. Scutum often has coloured designs.
Stigmata usually triangular. There are nearly always eleven marginal festoons
in the male.
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Hyalomma. —Eyes present, conspicuous. Rostrum long. Anal groove
opens anteriorly. Body elongate oval. Colour deep brown. Male with two
pairs of ventral shields, two large triangular perianal and two small external.
Scutum covering nearly the whole of the dorsum ; crenellated or festooned
posteriorly. Stigmata comma-shaped, having a long tail in the male and a
short one in the female.
The Argasidæ include only two genera: Argas and Ornithodoros.
Argas. —Eyes absent. The rostrum which is concealed by the cephalo-
thorax is situated at least its own length behind the anterior margin. There is
no fold round base of rostrum ventrally (camerostome). The body is oval or
orbicular. The integument not mammillated but covered with wrinkles and pits.
Ornithodoros.—Eyes present or absent. Rostrum surrounded ventrally by
camerostome (Pl. I., fig. 3.) The tips of the palpi visible from above. The
lateral borders of the body generally straight, sometimes concave. Tegument
mammillated.
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IV.
THE EXTERNAL ANATOMY OF TICKS.
T HE exo-skeleton of ticks has been very thoroughly studied by a number of
observers, notably by Neumann. 23It will be necessary only to point out
the chief structural features and to indicate the variations which may occur in
the different species.
Technique.—The examination of ticks for descriptive purposes cannot, as a
rule, be carried out without some special treatment, such as boiling or macerat-
ing in caustic potash, which serves the purpose of rendering the parts more
transparent. Such treatment is very apt to render the tick distorted and
difficult to mount satisfactorily. The following method obviates this tendency
and gives excellent results:—The tick to be examined is placed alive upon a
glass slip, and covered by a second slip. A rubber band, readily made by
cutting a short length from a rubber tube such as is used for bunsen burners, is
then slipped over either end of the two slips. The pressure of the glass will
cause the tick to assume an extended position, very suitable for examination.
A series of specimens may be rapidly put up in this way, and examined at leisure.
In this condition, and whilst still alive, a rough diagnostic examination may be
made. If it be desired to mount the tick without treatment in alkali, the glass
slips should be placed in alcohol until complete hardening of the specimen has
taken place. The tick is then removed, placed in fresh absolute alcohol, passed
through oil of cloves, and mounted in balsam. The specimen should be lowered
into a large drop of balsam which has been previously placed on the slide.
Otherwise air bubbles are apt to be troublesome. For the examination of the
mouth parts and other details of structure, it is necessary to plunge the tick,
still included between the glass slip, into 10 per cent. caustic potash. It may
be left to macerate for some hours or, what is usually to be preferred, it is boiled
for a time in the solution. In the case of soft-bodied ticks, especially gorged
nymphs and larvæ, it is necessary to regulate the pressure, or they may become
ruptured, either before or after placing them in the solution. Pressure can be
very conveniently regulated by cutting thinner or thicker bands of rubber and a
cover glass may be used in place of a slide. The proper degree of exposure
must be determined by the transparency of the specimen. It is important to
remember that this is increased on removing the specimen from the soda solution
to water. When the process of maceration, or boiling, is judged to be complete,
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the slides are removed and flooded in water. The rubber bands are then
removed, and the slips carefully separated under water by sliding one from the
other. The now decolourised tick is quite flat, and resembles a section. The
limbs and mouth parts are almost always in perfect position and well displayed.
It remains only to soak the skins in water and to pass through alcohol, and oil
of cloves, to balsam. If desired, the decolourised tick may be stained in weak
fuchsin, a procedure which shows up certain details very clearly, e.g., the teeth
of the hypostome. For exact descriptions of such structures as the cheliceres, it
may be necessary to dissect up the mouth parts, after boiling in caustic, and to
examine them in glycerine.
For Ornithodoros, prolonged boiling may be necessary, and for the display
of the mouth parts, it is very advisable to remove the dorsal integument prepara-
tory to treating with the caustic.
Very good specimens can often be obtained by utilising the cast skins of
young and medium-sized specimens. The only difficulty is that of removing air
bubbles. Heating in a large quantity of balsam before mounting will generally
get rid of these.
The Ixodidæ.—The Ixodidæ when not gorged are flat and more or less
disk-shaped in form. Anteriorly is the projecting " rostrum," equally visible
from the ventral and dorsal surface. From the lateral and under surface of the
body arise the legs, eight in number in the adult, but six only in the larva.
Behind the fourth pair of legs are the stigmatic plates. On the ventral surface
are the anus and the genital opening, the latter being situated a short distance
only behind the rostrum. The integument contains various hard plates
(schlerites) one of which, the scutum, covers a portion or the whole of the
dorsum, and the arrangement of which differs in different species and in the
sexes.
The external organs of generation are scarcely, if at all, distinguishable in the
two sexes, but the male and female ticks are, as a rule, readily distinguished by
the extent of the scutum, which in the male covers practically the whole dorsum,
whilst in the female it covers a small portion, at most one-third. The male also,
in most cases, is more ellipsoidal in shape and less regular in outline than the
female. The males of certain species also possess certain structures not seen
in the female, notably the anal plates, and in some cases, a rudimentary tail.
Marginal festoons are more marked in males, and they often possess tarsal
spurs which the female is without. (Fig. 6.) The females, on the other hand,
may have porose areas, structures not found in the larva, nymph, or male. The
females alone become gorged in the manner so characteristic of ticks. Nymphs
resemble the adult female more than the male and the scutum covers in them
only the anterior third of the dorsum.
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The Rostrum or Capitellum. —The rostrum consists of a massive posterior
portion (head) prolonged anteriorly into the mouth parts. The rostrum is large
and conspicuous in some genera, and may be extremely small, in comparison
with the body of the tick, in others. The head may be quadrangular, hexa-
gonal, or approximately globular. It is often prolonged laterally into a sharp
process. In some species it is received into a notch in the scutum, in which
case the scutum is said to be emarginate, in others the scutum is non-emargi-
nate. On the dorsal surface of the head of the female, in some ticks, are two
curious, bilaterally-situated, perforated areas (Porose areas). Fig. 2.
The dorsal surface of the head is continuous with two tubular sheaths,
within which the rod-like mandibles (Cheliceres) play. Ventrally the head is
continued forwards as a conspicuous dagger-shaped process (Hypostome). On
either side of the cheliceres and hypostome are the jointed palps (pedipalpi).
The hypostome, cheliceres, and the pedipalpi lie as a rule closely approximated.
In the genera in which the palpi are long, they are often found separated from
the rest of the mouth parts. Where the palpi are very short and broad, as in
Rhipicephalus, this separation is rarely seen.
The Hypostome (Fig. 1. H).—The hypostome is continuous with the
chitinous exo-skeleton of the head. It is always more or less dagger-shaped
though the point may be rounded. The ventral surface carries a number of
conspicuous teeth, directed backwards, and usually arranged in several rows.
The number of longitudinal rows of teeth is very constant in the same species
and is used for identification. Small rudimentary teeth the arrangement of
which is irregular are often present about the tip.
The Cheliceres (Figs. 1 and 2).—The cheliceres are strongly chitinised
organs, the anterior portions only of which are seen on external examination.
The posterior halves, which are swollen, lie in the body cavity, where they
receive the attachment of powerful muscles. The anterior portions are rod-like
and play each in a sheath, formed by a prolongation forwards of the chitinous
covering of the head. The sheaths are lined with a loose membrane, and are
covered externally in most cases with fine ridges or teeth. At their termination
the cheliceres carry a jointed process (digit). The digit carries several pro-
cesses (apophyses), which bear large hooked teeth directed backwards. Some
authors attach considerable importance to the number and arrangement of these
teeth, but Salmon and Stiles state that they are subject to variation in the same
species and of doubtful value in identification. The bulbous posterior portion
of the cheliceres contains muscles ending in tendons, which are inserted into the
digit. The cheliceres may be retracted within, or extruded from, their sheaths
by the action of their associated muscles.
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