NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
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The duct is surrounded by small clear cells with small nuclei. Where the
duct enters the acinus, there is a large cell with finely reticular protoplasm,
which appears never to contain granules, and is probably of a different character
from the other cells of the acinus (Pl. IV, fig. 3 a). It has a distinct and large
vescicular nucleus.
The glands in the larva and nymph.— A good deal of interest attaches to
the development of the salivary glands and their condition in the younger stages
of ticks. The salivary glands, as first seen in the embryo, consist of a short
straight tubule surrounded by large cells. The cells increase in number and
form bud-like outgrowths, to each of which a short blind diverticulum from the
duct afterwards passes. The buds form a single row of rudimentary acini.
Three or four only of these become at all developed in the larva. The
immature acini are seen in fresh preparations as clear transparent structures
showing a small number of cells arranged around a central lumen. There is
often to be made out a delicate inner lining to the cells. The duct appears at
first not to communicate with the lumen of the acinus but later lateral offshoots
are seen going to each acinus. In section, the cells of the immature acinus have
rather darkly staining protoplasm and large conspicuous nuclei. Supporting
cells are seen, which appear about to become a capsule.
At the time of casting the larval skin, about fifty acini are present. These
form a single row only and each leads by a short duct directly into the central
tubule. At this time granules, resembling those seen in the adult, are already
present in some of the acini.
The rectum and malpighian tubules. —(Pl. III, fig. 8).—The rectum, which
lies immediately behind the spermatheca, or the white gland in the male, is an
irregular sac having several capacious but short saccular dilatations. It receives
the rudiment of the intestine and the two malpighian tubules. Its walls are
extremely thin and consist of a single layer of flattened cells. It contains
a white fluid, which is identical with the secretion of the malpighian tubules.
The rectum in ticks therefore does not serve as an adjunct to the alimentary
canal, but functions as an excretory receptacle. The white matter passed per
anum by ticks also cannot, strictly speaking, be regarded as fæces.
The malpighian tubules are important, not only on account of their great
length and functional activity in ticks, but also from the frequency with which
in other animals such organs are utilised by parasites, and from the fact that
Dutton and Todd have traced the spirochætes of "tick fever" to these tubes.
They consist of two fine white or transparent tubules of great length, which
arise on either side from the rectum, and after a complicated course among the
viscera, end blindly in the anterior portion of the body. Near their origin from
the rectum they lie upon the ventral surface of the body, and come in relation to
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many muscular bundles and the posterior diverticula. They then pass to the
dorsum and form a number of convolutions in the posterior portions of the body.
From this situation they pass forwards over the dorsum in close relation with
the ovary and dorsal vessel and are abundantly supplied by the dorsal tracheal
branches. Whilst passing over the dorsum they are visible during the period
of oviposition as white or yellow streaks. Dipping down by the oviducts they
come in close relation with the posterior lateral diverticula. They then pass
outwards beneath the free end of the salivary gland, cross the anterior ventral
trachea, and lie among the anterior and middle diverticula of the lateral series.
After making several convolutions they end blindly, generally over the anterior
lateral diverticulum. It will therefore be seen that during their course the
tubules come in relation with almost every important organ in the body and drain
every quarter of the body cavity.
The tubes in young ticks are of an even calibre throughout, and contain
small quantities only of secretion, but they are often seen, specially in aged
ticks, swollen here and there so as to form sacs similar to, but smaller than, the
rectum. When oviposition is complete, the tubes and the rectum may be greatly
distended with the characteristic white fluid, and may, especially the latter, be
evident externally as patches of lighter colour. It is possible that the appear-
ance is that described as a " fungus " in these ticks by Wellman20.
Structure of the malpighian tubules. —(Pl. IV, fig. 4).—The tubules consist
of a single layer of large cells arranged upon a basement membrane. In
Ornithodoros the cells exhibit considerable irregularity in size. They are cubical
or columnar in the undistended organ, but become flattened in the distended
state. The cells show, when deeply stained, markedly striated protoplasm.
The nuclei are very large and of vescicular nature. The lumen of the tube
always contains characteristic crystalline bodies, which in mass give rise to the
dead white colour of the secretion of the tubules. The crystals are circular, or
more often oval in shape, and often exhibit a marked " dumb-bell " appearance.
They are of various sizes reaching 10 µ. in diameter. They show fine radiating
lines in their substance. These crystals have been present in every species of
tick which I have examined, and they are seen even in the embryo of Orni-
thodoros before blood has been ingested. They undoubtedly represent the
condition in which waste matter is mainly excreted by the tick. They are
slightly soluble in acids, but readily soluble in strong alkalies. Their chemical
composition is probably similar to that of uric acid.
The ovaries and female organs of generation. —(Pl. III, fig. 8, and Pl. IV,
figs. 5 to 10).—The ovary is a single organ opening at either side in an oviduct.
In Ornithodoros it is comparatively short and broad, and lies obliquely across the
abdomen, just behind the mass of the central alimentary sac, and over the origin
39
of the posterior series of diverticula. It lies directly beneath the expansion of
fat tissue and tracheal branches, which cover the viscera dorsally, and in close
relation with the dilated posterior portion of the heart, and the malpighian
tubules.
The oviducts are long coiled tubes, very delicate where they arise from the
ovary, but becoming denser and stouter as they near their termination. A short
distance from the ovary there is an enlargement, the significance of which is not
clear. On reaching the root of the spermatheca, the oviducts become very
thick, and after forming a loop on either side, they enter the substance of this
organ, and give to it the characteristic bicornuate appearance.
The spermatheca is a large sac possessing thick walls. If it be opened up,
transparent cystic bodies (spermatophores) will be found free in its cavity.
Anteriorly the combined duct of the spermatheca and oviducts passes
forwards, lying close to the ventral surface, towards the genital opening. Just
before its termination, it becomes thicker and of an opaque white colour. In
this portion of its extent it receives some muscular bundles from the endoster-
num ; upon this portion also lies the central ganglion and a plexus of tracheæ.
The ovary differs in structure entirely from those of insects, and there are
no follicular tubes as in this class. The ovary in Ornithodoros is essentially a
fusiform thin-walled sac, continued at either end into the oviducts. The wall of
the sac shows a differentiation into two areas—a dorsal area which gives rise to
ova, and a ventral area which has no such function. The dorsal area forms the
greater portion of the ovarian sac as usually seen. It is studded over, in more or
less regular lines, with ova in different stages of development The ova, except
when quite mature, project freely from the outer surface of the ovarian wall.
The youngest cells are situated near the edges of the dorsal area, where this
passes into the membrane of the ventral surface. The ova, of which there are
about ten rows, increase in size as they are situated, further from this situation.
The ventral area is composed of a very thin greatly wrinkled membrane. In the
undistended state of the ovarian sac, this membrane occupies a small portion
only of the circumference. Owing to the extent to which it is folded it is
capable of being very greatly stretched. It is therefore more clearly seen when
the ovary is distended by the presence of a number of large mature ova in its
cavity (Pl. IV, fig. 5 b ).
The youngest ova are large cells, having extremely large and deeply
staining nuclei and a small amount of protoplasm.
More mature ova are large globular or oval cells, having granular or reti-
cular protoplasm, which stains deeply with hæmatein. Afterwards the protoplasm
becomes filled with globules which increase in number and size rapidly as the ovum
matures. The nucleus is large and vescicular. It contains one or more darkly
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staining masses, which show a varying arrangement. The nucleus, as a rule, lies
close to the attached end of the cell.
The ova, as they increase in size, project boldly from the surface of the
ovary. After reaching a certain size, they become provided with a funicle,
composed of altered cells of the ovarian wall. These cells are cubical or
columnar, and merge at the base of the funicle with the ordinary, rather flat,
cells of the ovarian wall. In the distended ovary, the funnel-shaped funicle is
flattened out. The funicular cells then form a flat plate, upon which the now
tightly bound down ovum lies. When the ova become mature, they are found
lying free and unattached in the lumen of the ovary. Quite how the change is
effected, by which the large ova at the end of a funicle come to be within the
lumen of the ovary, is not known, as intermediate stages are not often seen.
The process would appear to depend on a flattening of the funicle by the
pressure and growth of the large ovum, and the eventual forcing open of the ring
of cells by the same means.
It is not uncommon to see, in the protoplasm of ova of a certain size, the
remains of one of the huge spermatozoa, which characterise Ornithodoros.
Spermatozoa are present in the ovarian sac, and it appears likely that fertilisation
often takes place in this situation.
The fully mature ova, as they are seen after passage into the cavity of the
ovary, are globular, of a rich brown colour, and a millimetre in diameter. Their
protoplasm is densely packed with droplets of an albuminoid matter and with
fine granules. The nucleus is no longer visible. Attached to the ovum at this
time there is a curious structure the origin of which is doubtful (Pl. IV, fig. 7).
The oviducts (Pl. IV, fig. 11) are lined with long columnar cells, having
clear protoplasm and rather large nuclei, situated near the basal portion of the
cell. The outline of these cells is irregular, and they resemble in general
appearance the cells lining the œsophagus. External to the epithelial layer are
fibres of a muscular nature, and outside these a layer of curious large polygonal
cells with large nuclei. The lumen of the oviduct, especially in its lower
portions, is distended with masses of gigantic spermatozoa, which often exhibit
active and characteristic movements. The spermatheca is similar to the oviducts
in structure. It contains a number of spermatophores. The spermatophores
are bean-shaped or globular cysts, packed with spermatozoa. They have a
hollow stalk, from which the spermatozoa are discharged when pressure is made
on the cyst.
The spermatozoa will be described later ; but it may be mentioned that in the
female they are in a more advanced condition of development than when in the
male.
The male organs of reproduction. —(Pl. V, fig. 6.)—Occupying the position
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taken by the ovary in the female there is, in the male, a delicate, thin and trans-
parent tubule, ending upon either side in a coiled duct, which much resembles
the oviduct in the female. The tubule referred to is from its anatomical relations
evidently the testis. It is usually, however, in much of its extent devoid of
reproductive tissue. The ducts at either side are, on the other hand, packed
with cells in all stages of spermatogenesis. The youngest spermatogenetic
tissue is situated in the upper and narrow parts of the lateral ducts, whilst later
stages are seen in their lower portions. There is not, however, a regular
gradation of development from the upper to the lower parts of the tube, and
tissue in an advanced stage may be situated higher than other less mature tissue.
In the other parts of the duct very young spermatogenetic tissue is seen
consisting of a stroma of small branched cells enclosing in its meshes from four
to six comparatively large cells. These cells have deeply staining protoplasm and
large conspicuous nuclei. The stroma cells, which are branched attenuated
cells with small nuclei, are attached externally to the wall of the duct. Inter-
nally they are arranged so as to leave a central lumen. Between the lumen and
the wall, they form loculi, in which the nests of spermatogenetic cells lie.
The cells lying in the loculi, which are at first comparatively small, increase
in size until the cells of a single nest occupy the whole lumen of the duct. The
stroma cells then disappear, whilst the spermatogenetic cells arrange themselves
around the wall of the duct and become attached to it. The cells at this stage
are very large and conspicuous, having deeply staining reticular protoplasm
and conspicuous nuclei. They soon begin to show further changes. At the
outer margin, a curious clear area appears, and rapidly increases in extent.
This area appears to be due to a dropsical degeneration of this part of the
cell. As the condition progresses, the protoplasm of the cell is pushed
inwards, being connected with the outer wall only by strands of its sub-
stance. About this time, a cap of very dark staining material appears over
the inner surface of the cell, and eventually extends all around it. The nucleus
which was at first conspicuous, becomes during these changes difficult to trace.
It appears wholly, or in part, to pass to the surface, for a small very dense mass
is now seen surrounded by a clear area lying in this position. The appearance of
this nuclear mass on the surface determines the formation of one, or possibly
more, buds, which, after a complicated development, become spermatozoa. The
original cells, whose history we have briefly sketched, would appear to be homo-
logous with the mother cells of the spermatozoa of the earth worm. An interest-
ing fact is the small number, usually only one, of spermatozoa which these cells
eventually give rise to.
The Spermatozoa. —(Pl. V.)—These are seen in a fully mature condition
only in the female. In the spermatheca and oviducts of the female, Ornithodoros
G
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they are seen as relatively immense club-shaped bodies, and are visible as
minute rods to the naked eye (Pl. V, fig. 1). Examined fresh they are very
transparent. They may be motionless, or may exhibit a steady gliding
movement, together with marked vermicular contortions of the anterior portion
of their substance. Anteriorly there is a thick bulbous portion, which occupies
about one quarter of the total length of the structure. Posteriorly there is a
thick tubular tail. Around the extreme anterior tip there is a lip, such as is seen
in some filarial embryos. Still further back there is, embedded in the substance
of the spermatozoön, a basket-like arrangement, consisting of fine longitudinal
lines arranged in the form of a truncated cone (Pl. V, fig. 2). Posteriorly there
can usually be seen in the tail two fine filaments. At the extremity there
is a tag containing a refractile mass. This tag may be included in the tail or
exposed.
The spermatozoa stain with difficulty. Stained with hæmatein they show
a large, somewhat lightly staining, mass in the situation of the cone of lines
already described. Posteriorly there is darkly staining body, which is that
already described in the tag attached to the posterior extremity. The two
filaments in the tail also stain (Pl. V, fig. 1).
The spermatozoa in the oviducts are free in the lumen. In the spermatheca
they are for the most part included in the cyst-like spermatophores. In both these
situations the majority of the spermatozoa show the characters described above.
In the males the spermatozoa are rarely seen in the above condition, but
are invaginated upon themselves, so that they are spindle-shaped and about half
the length of the extended structure. This curious condition arises from the
method in which the spermatozoa develop (Pl. V, fig. 4).
The buds which arise from the mother cells, are anchored by a short stalk
at the base of which is the dark granule already mentioned as probably derived
wholly or in part, from the nucleus of the mother cell. At the time when the
bud has fully formed, this body has passed out of the substance of the mother
cell to be in the stalk as noted.
The spermatoblast, which consists of finely granular protoplasm, contains
a clear vescicular area of the nature of a nucleus. On the side corresponding to
the unattached surface of the spermatoblast, the vescicular area gives rise to a
flat prominence. At the opposite pole a conical papilla arises. The sper-
matoblast and the vescicular area both elongate, whilst the latter shows some fine
spiral lines. The originally flat prominence grows out so as to form a long
tail. The conical outgrowth of the vescicular area becomes shaped as the
head of the adult spermatozoon, and shows a lip as in this structure. Around
this end the remains of the protoplasm of the spermatoblast is gathered. The
head then invaginates into itself and carries with it the residual protoplasm and
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even the nuclear mass in the stalk, which becomes eventually the dark staining
body in the tag of the posterior extremity.
Spermatozoa are sometimes seen which have become so invaginated and
plicated as to form globular structures. The various steps in the invaginations
are rather difficult to follow.
The white glands of the male. —The lower parts of the male ducts are much
swollen from the masses of spermatozoa which they contain. They eventually
enter a large white lobulated structure, the white gland (Pl. V, fig. 17). The
white gland consists of two lateral portions, and a central portion of similar
appearance, but of different structure. The lateral portions are merely the conti-
nuation of the male ducts, which here become still more dilated. The central
portion is glandular in nature. It consists of a double lobulated sac. The walls of
the sac, in certain narrow portions of the organ, are composed of columnar cells
of extreme length (Pl. V, figs. 18 and 19). In the more swollen portions of the
sac, nothing but a mass of albumenoid granules can be made out. It is possible
to trace all gradations between the long columnar cells and the final condition in
which these have become wholly transformed into the granular substance. The
white gland is probably concerned in the elaboration of the spermatophores.
The muscular, tracheal, nervous and circulatory systems. —The muscular
system in Ornithodoros is well developed. The muscular bundles of the body
may be classed as follows :—
( a ) Muscles of the mouth parts.
(b) Muscles of the limbs.
(c) Muscular masses of the body.
(d) Muscular masses connected with the entostermum.
(e) Visceral muscles.
Of the first group we have already noted the muscles lying in the cavity of the
cheliceres, which move the digits and apophyses, and those which pass from the
dorsal integument to the cheliceres. The muscles acting upon the pumping
organ form a dense mass around this structure, and practically fill up the whole
of the space of the head beneath the endoschlerite. The muscles of the second
group require no special mention in a paper of the present character. Muscle
bundles of the third group pass for the most part between the ventral and
dorsal surfaces. They lie between the diverticula and support these by forming
pockets in which they lie. A conspicuous mass passes up on either side of the
spermatheca. Another extensive series lies behind this organ, whilst a third
takes its origin from the ventral surface behind the rectum. Fibres from the last
two series, as well as passing upwards to the dorsum, pass out to be inserted
laterally. Similar dorso-ventral bundles pass between the diverticula in the
anterior portion of the body.
G 2
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The entosternum is densely clothed in muscles which pass in almost every
direction to be inserted into the integument and viscera. Specially strong
bundles pass out laterally.
The visceral muscle fibres are of a curious type. They show no striations
but differ widely from the unstriated muscle of mammals.
The tracheal system is well developed. From the spiracle a leash of tracheæ
pass inwards. The tracheæ may be divided into dorsal and ventral branches.
The dorsal branches are small. An anterior dorsal branch passes inwards to
help in the formation of the dorsal tracheal meshwork, a posterior dorsal branch
supplies especially the malpighian tubule and ovary. The ventral branches are
much larger, a very large trachea [anterior ventral] passes outside the base of
the legs to the anterior portion of the body, where it joins its fellow of the
opposite side above the rostrum. At its origin it gives off a large branch which
passes in to supply the structures about the entosternum, and to help to form
the tracheal ganglion. Just before reaching the salivary gland, it sends a large
branch to supply the head and other structures. Besides supplying the salivary
gland, it sends branches to the first two pairs of legs. In connection with the
branches of this trachea there is a plexus, or tracheal ganglion, beneath the
central nerve ganglion and lying over the genital opening.
Another large trachea of the ventral series passes directly inwards to supply
the muscles and viscera in the neighbourhood of the spermatheca. A third
branch of smaller size supplies the muscles and other structures behind the
rectum.
A single nervous ganglion only is visible in dissection. This lies
upon the final portion of the common genital canal, and is pierced by the
œsophagus. It sends branches outwards to the limbs, and along the œsophagus
to the viscera. The structure is similar to that of ganglia in insects, consisting
of an inner portion of non-medullated fibres and an outer zone of nerve cells. In
comparison with the body of the tick it is of very small size.
The circulatory system is poorly developed. There is a median heart with
a dilatation posteriorly. In the young tick this can be seen actively pulsating.
Anteriorly the dorsal vessel divides into two branches which dip down in front of
the diverticulum to come in relation with the nervous ganglion. Their course is
difficult to follow.
The heart in fresh preparations is a transparent structure, having small
clusters of granular cells attached to its inner surface. It is abundantly supplied
with tracheæ which form long wavy branches. Fine transparent fibres, prob-
ably of a muscular nature, are seen in, and attached to, its walls. During the
period of oviposition in Rhipicephalus large cells, resembling the adventitious
cells of the fat body, have been observed in close connection with the heart.