NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
45
The fat body. —The fat body in insects is recognised to play an important
part in nutrition and assimilation. In ticks it consists of numerous trabeculæ,
which, bound up with tracheæ, form a loose cellular material. This material lies
in among the organs, but is specially abundant about the origin of, and along the
course of, the larger tracheal vessels. A somewhat different tissue of a more solid
nature occupies certain spaces such as those of the head, pedipalps, and limbs.
The fat body in ticks is a complex tissue and is composed of several forms
of cells. It has been by no means well developed in specimens of Ornithodoros
which I have dissected, and it will therefore be more convenient to describe its
structure as displayed in Rhipicephalus, where it forms a prominent tissue. So
far as could be seen, the tissue in Ornithodoros was essentially of a similar nature.
The integument and dermal glands. —The integument consists of a basal
cellular portion composed of a single layer of columnar cells and a superficial
chitinous layer. In Ornithodoros the chitinous layer forms a number of pa-
pillomatous-like outgrowths with a hollow core. In Rhipicephalus the columnar
cells of the dermis are extremely large and conspicuous.
There are a number of glandular structures of dermal origin.
(1) The coxal gland. —These are large, flask-shaped organs, very abun-
dantly supplied with tracheæ, which lie upon the second coxal joints, and open
by a small pore upon the coxal joint of the first pair of legs. They secrete
an abundant clear fluid, which is slightly alkaline and prevents the coagulation of
blood. Their presence in Rhipicephalus and Hyalomma has not been ascertained.
They appear similar to the coxal glands of Scorpio, as described by Lankester.
(2) The cephalic gland.—This remarkable structure which I have so named
is of large size, lies above the head and beneath the anterior diverticulum. It
consists in Ornithodoros of a double plicated sac, with a large cavity opening on
the surface by an extremely wide duct, the position of which has been described
already. In section it is seen to consist of a single layer of very regular columnar
cells, which may contain droplets of fat. The lumen is usually devoid of contents.
RHIPICEPHALUS.
In Rhipicephalus and Hyalomma the mouth parts are proportionately small
in comparison with the alimentary canal and its diverticula. In the main the
parts are similar to those of Ornithodoros but the relation of the cheliceres to
the pumping organ is different (Pl. VI, fig. 10). Posteriorly the canal opens
freely into the rectum, but it is doubtful if material ever passes directly from
the sac to this organ.
The system of diverticula is in the main similar to that already described
in Ornithodoros, but in Rhipicephalus the structure of the diverticula is simpler
and shows more clearly the plan upon which their arrangement is based.
46
The anterior diverticulum is not present. The lateral series arise from
the anterior extremity of the central sac on either side as a single trunk
from which arises an anterior middle and posterior branch. The anterior
branch passes forwards to the anterior portion of the body. It is often
supplemented by one or two small accessory branches (Pl. VI, fig. 4 a, b).
The middle branch occupies most of the lateral regions of the body lying
in front of the stigmata. The posterior branch passes down in the neighbour-
hood of the stigma, and then forwards and inwards to end in front of the genital
opening, almost touching the base of the rostrum, and close to, if not in contact
with, its fellow of the opposite side.
From the origin of two anterior common trunks the central sac passes
backward as a straight cylindrical organ to the level of the anus. At this point
two diverticula arise on either side. The inner pair are comparatively short and
after passing backwards bend forwards on the ventral surface to reach the
neighbourhood of the anus. The outer pair are longer and continue onwards
almost as far as the genital opening. From the origin of the posterior series the
central sac bends sharply downwards to end in the rectum.
The chief differences between Ornithodoros and the present genus lie in a
greater complexity of arrangement in the former and in the possession of an
anterior and posterior median diverticulum, which are not represented in the latter.
The existence of at least an anterior (lateral of the above description) and pos-
terior series of diverticula in ticks appears clear. Whether both are homologous
with the so-called "liver" of the Arachnidæ I am not at present able to say.
As they both lie in the post somatic region it would rather seem that this is
the case.
The salivary gland in Rhipicephalus occupies a similar position and is
essentially of the same nature as in the Ornithodoros. The acini are, however,
much more loosely held together, and the whole organ is less compact than in
this genus (Pl. VI, fig. 7). The structure of the acinus is also much simpler,
and shows more clearly the real relation of the acinar cells. Sections show the
acini to be lined with a single layer of large cubical cells having clear protoplasm
and large vescicular nuclei. About six to eight cells are shewn in cross section
(Pl. VI, fig. 8). Some of the cells are larger than others and possess granules.
The malpighian tubules resemble those of Ornithodoros and have similar
relations to the organs. The importance of the tubules as excretory organs is
well shown by the changes which occur at the period of oviposition in Rhipice-
phalus.I n a r e c e n t l y r e m o v e d g o r g e d t i c k t h e t w o l o n g t u b u l e s c a n b e s e e n t o
have scattered throughout their length, a certain number of crystalline bodies,
whilst the rectum is moderately distended. A few days after removal of the fed
tick from its host, the malpighian tubules will be found much more opaque
47
from contained secretion, and they may be dilated here and there into little
white sacs. As oviposition advances the tubules and rectum become extremely
voluminous, and vie with the blood sacs in size. Eventually the body of the tick
consists mainly of these organs. The immense amount of waste matter
accumulated by the malpighian tubules in a comparatively short time points
to a very rapid and active metabolism during this period.
The generative organs of Rhipicephalus, though in general arrangement
like those of Ornithodoros, differ somewhat in detail. The ovary is much more
elongated and lies in the form of a long U in the body cavity (P1. VI, fig.
11). The oviducts are less conspicuous, except at the period of oviposition
than those of Ornithodoros. The spermatheca is small and of simple construc-
tion (Pl. VI, fig. 13). It forms a simple globular sac opening at the junction of
the oviducts into the common genital canal. It contains several spermatophores,
which can be seen with their tubes lying directed towards the opening of
the sac.
In Rhipicephalus there is a tubular gland, opening on either side of the
opening of the spermatheca, which appears to be absent in Ornithodoros. The
structure of this gland calls to mind the mucus glands found in connection with
the genital apparatus of many insects.
At the time of oviposition, the oviducts become enormously elongated and
form convoluted masses lying upon either side of the anterior portion of the body.
Ova are placed at regular and close intervals along their lumen.
The spermatozoa of both Rhipicephalus and Hyalomma are similar in shape
to those of Ornithodoros, but they are much smaller being only about one-third
the length (Pl. VI, fig. 12). There are also some small differences in the shape
and in the movements of the head. Whilst the head of the spermatozoan of
Ornithodoros exhibits writhing movements those of Rhipicephalus show an
extraordinary buckling up movement, alternating with a sudden and violent
straightening action.
Mention has been made in the case of Ornithodoros of a curious gland, the
cephalic gland. A similar organ is present in Rhipicephalus and is of even
larger size. It consists, however, instead of a plicated bag, of a number of long
finger-like diverticula which are conspicuous both in careful dissections and in
sections (Pl. VI, fig. 5, e.g. ). In structure the gland is similar to that of the
plicated bag of Ornithodoros. The presence of so large a gland has led me to
examine ticks for the external opening. In Ornithodoros this is readily found, in
the Ixodinæ it is less conspicuous but can in some cases be detected. If the
rostrum of Hyalomma, which is large, be forcibly bent downwards, so as to lie
upon the venter, the floor of the fold between the rostrum and the scutum will be
exposed. By means of a lens it is possible to make out in this situation an
48
inverted V-shaped mark, which appears to be a pore with slightly thickened
edges, but I have not succeeded in passing even the finest hair into this opening.
The homology and function of this gland, which has not, so far as I am aware,
been hitherto described, are obscure. Its large size would lead one to suppose
that it served some important functions.
In addition to this organ, there are in ticks a number of small glands
undoubtedly of dermal origin lying in the fat tissue. These are small globular
bodies, readily seen with a lens. They consist of two gigantic cells lying in a
capsule. Fatty degeneration commences at one or more spots and may
eventually convert the whole into a mass of minute oil globules (Pl. VI,
fig. 2 c ). These structures, which appear to be oil glands, have not been
detected in Ornithodoros. In hyalomma they are particularly prominent and
one may be led to suppose that they are parasitic in nature.
Opening upon the surface in the neighbourhood of the rostrum there are
also some simple acinar glands containing cells of remarkable histological
character. Examined in the fresh state they are seen to be composed of
enormous cells containing a large vescicular nucleus and a vacuole with a double
contour. In section they show a reticular protoplasm and extremely large
darkly staining nuclei. The border of the vacuole stains faintly with hæmatein
(Pl. VI, fig. 3). These glands lie just beneath the integument of the rostrum
and are rather prominent in sections through this organ (Pl. VI, fig. 10 d, g).
They have not been detected in Ornithodoros.
The fat body in the gorged female of the Ixodidæ is an important tissue.
It is specially prominent over the dorsum and in the neighbourhood of the
tracheal leashes. The main bulk of the fat body is composed of trabeculæ,
formed from polygonal or cubical cells arranged in rows. In certain of these
cells the protoplasm is drawn out so as to end in a fine filament, and these
act as sustentacular cells by mooring the trabecula to the body wall or other
structure. The trabeculæ may be of considerable length, and yet consist of a
single row of cells only. In some cases more solid lobular masses are formed,
but pads and lobules of the tissue are not characteristic of the tissue in ticks.
The cells which compose the trabeculæ may show finely granular protoplasm, or
they may be more or less replete with oil globules. As a rule the tissue is not
so charged with fat as is the fat body in insects. The sustentacular cells are
similar in all respects except in the possession of a filament and in their
elongate shape.
Attached to the trabeculæ are cells of an entirely different nature. These are
large oval or round cells containing as a rule yellow droplets (Pl. VI, fig. 1 d ) .
In addition to the typical fat body substance which is normally composed
of the two varieties of cells, just mentioned, there is in ticks a good deal of cellular
49
tissue, the exact nature of which it is difficult to determine. Accompanying the
branches of the tracheæ are certain free, comparatively small, oval cells. In the
same situation are very large cells with deeply stained granular protoplasm.
In connection with muscle there are masses of small cells, having processes
somewhat like the prickle cells of the human epidermis. In among the trabeculæ
of the fat body dermal glands may be encountered.
H
50
VI.
THE STRUCTURE OF THE OVUM AND THE EMBRYOLOGY
OF TICKS.
T HE ovum of Ornithodoros , when laid, possesses a structureless shell very
resistant to the penetration of fluids and even of alcohol. Within the shell
is an extremely delicate membrane, which can sometimes be made out in dissec-
tions. This membrane encloses a mass of yelk. The yelk is mainly composed
of globules of a substance which in sections stains faintly and uniformly with
hæmatein, and which appears to be albumenoid in nature. The globules are
separated from each other by a trace of more darkly staining granular material.
A few days after oviposition the upper surface of the ovum may shew, under
a lens, certain pale translucent spots. These increase in size, whilst others
appear, until an opalescent patch, clearly visible to the naked eye, is formed,
covering about half the area of one hemisphere. Shortly afterwards the egg shell
ruptures, and the globular larva emerges. Examined in detail, the changes at
this time are as follows :—
FIG. 7.
I. First appearance of germinal layer.
II. Appearance of rudiments of limbs and tail.
III. Embryo just before hatching. g= ganglion ;
r=rudiment of rostrum.
IV.& V. Formation of alimentary diverticula from
yelk. Dorsal view of ovum and newly
hatched larva.
The first sign of the formation of the young tick is seen in the presence of
three pairs of small translucent spots and one single median spot of larger size,
5
arranged as in the figure (Fig. 7). The paired spots increase in size, elongate,.
and approach each other in the middle line. They represent the rudiments of the
first three pairs of legs. Other translucent spots make their appearance, a central
and two lateral spots showing the future position of the rostrum. A pair of spots.
anterior to the rudiments of the first legs, and a pair posterior to the third legs,
possibly represent the pedipalps and the fourth pair of legs. The last mentioned
spots become obscured and are not visible in later stages. A large pale area, the
rudiment of the ganglion, appears in the middle line, just behind the rostrum, and
between the rudiments of the legs. Some characteristic crystals are already
deposited in the region of the rectum, and give rise to a white spot. The large
median spot, which forms the point of the V in the arrangement first seen, take up
a more and more dorsal position, whilst another median spot rather broad and
diffuse appears in front of this and apparently represents a tail, which is not sub-
sequently developed. At the time of hatching the condition of the young tick is
FIG. 8.
I. Dorsal aspect of larva immediately after hatching.
II. Ventral aspect of the same.
R =rostrum ; B=the remains of the large polar spot ;
G =rudiment of ganglion ; Re=rectum.
still markedly embryonic. The rudiments of the three legs are distinct, and form
conical, rather elongate, projections. The rostrum though imperfectly formed
is clearly indicated. The oval rudiment of the ganglion forms a very conspicu-
ous object, as does the collection of excretory crystals in the neighbourhood of
the future rectum. Dorsally there is a pale area, the shrunken primitive unpaired
spot. From this, as a centre, lines pass out in a radiating manner, which form
constrictions of, and divide up, the yelk into lobules. The constrictions already
distinctly mark out an anterior, three lateral, and two posterior areas. Ven-
trally the lobules of the yelk come into distinct relation with the bases of the
rudimentary legs. Thus a lobule is present on either side of the rostrum,
another lies opposite the base of each of the legs, whilst behind the third leg a
pair of lobules on each side curve round towards the midventral line. Posteriorly
H2
52
four lobules curve round from the dorsal surface and approach the rectum and
lateral lobules. Thus the yelk of the ovum represents, in a direct manner, the
alimentary sacs of the adult. The remains of the pale spot on the dorsum, from
which, as a centre, the constrictions of the yelk take place, represent very exactly
the future position of the dilated portion of the heart. The spot is very possibly
the blastopore and as such may be connected with the formation of hypoblastic
tissue.
In sections, the embryo is seen as a disk of very small cells, which stain
intensely with hæmatein. The rudiments of the legs and rostrum are hollow
outgrowths of this layer. The rudiment of the ganglion is early seen as a con-
spicuous mass of cells, and in the larva this organ is relatively of immense size.
Muscular fibres, lying especially around the circumference of the yelk, and
passing from the dorsal to the ventral surface, are early seen, as also are the
crystals of excretory matter. These lie in the yelk in the neighbourhood of the
future anus. Short malpighian tubules are seen lying along the ventral surface.
At the hatching of the larva the pharynx is seen as a tube, lined by a single
row of cubical cells surrounded by radiating cells of a filiform shape, evidently
rudimentary muscle fibres. The salivary glands are also present at this time,
and consist of some darkly staining cells arranged in groups around a fine central
duct. A short straight œsophagus pierces the ganglion, and comes in contact
with the yelk. The yelk, as development progresses, becomes more homo-
geneous in structure. Large cells with an open reticular protoplasm are seen at
its periphery, and these multiply and clothe the lobules. In the nymph much
yelk still remains in the alimentary canal. The muscles of the limbs are clearly
seen in the larva. Around and among them are round or oval cells, containing
retractile granules in their protoplasm. These cells appear to migrate into
the limbs from the body of the embryo. They undoubtedly represent the first
rudiment of the fat body tissue.
The most important fact from a parasitological point of view is that the yelk
of the ovum actually becomes the system of alimentary sacs in the adult. Even
if the cells, which form the walls of the sacs, are derived from other sources,
it is still evident that the alimentary sacs of the nymph of Ornithodoros contain
the remains of the yelk of the ovum. The pharynx, œsophagus, and salivary
duct are formed from an ingrowth of the outer layers of the embryo. The
origin of the acinar cells is doubtful, and it is possible that they are mesoblastic
in origin. The malpighian tubules seem to be formed from cells in connection
with the yelk : it is difficult otherwise to understand how their secretion comes to
lie actually in contact with this substance.
In Rhipicephalus the amount of yelk in the ovum is relatively small. The
early stages of development are similar to those in Ornithodoros. The later pro-
53
cesses have not yet been followed. It is probable that the relation of the yelk
to the alimentary sacs of the larva is similar to that described in Ornithodoros.
A curious feature of the ova of Rhipicephalus is the frequency with which
ova contain, or are filled with, what appear to be crystals of fatty acids. I have
never found a trace of blood within the shells of eggs deposited by ticks of any
of the genera described in this paper, and it is probable that the statements
upon this subject which are to be found in several text-books require revision.
54
PAPERS REFERRED TO IN THE TEXT.
1. Smith and Kilborne. Texas Fever. Washington Bulletin No. 1, 1893.
2. Koch. Reiseberichte über Rinderpest, etc. J. Springer, Berlin.
3. Theiler. East Coast Fever. Journ. Royal Army Medical Corps,
December 1904.
4. Donitz. Die Zecken des Rindes als Krankheitsüberträger. Sitzungs-
berichten des Gesellschaft naturforschender Freunde. Jahrg. 1905, No. 4.
5. Motas. Sur le rôle des tiques dans le developpment de la piroplasmose
ovine (Carceag). Comptes rend. soc. de biol., t. LV., pp. 501-504.
6. Bowhill. Equine piroplasmosis or biliary fever. Journal of Hygiene,
Vol. IV, 10 January 1905.
7. Lounsbury. Transmission of Malignant Jaundice of the Dog. Report
of the Govt. Entomologist (Cape Colony) for 1903. Reprint in Journal of
Comp. Pathology and Therapeutics, June 1904, Vol. XVII, part 2.
8. Nuttall. Canine Piroplasmosis. Journal of Hygiene, Vol. IV, No. 2.
April 1904.
9. Marchoux and Salimbeni. La spirillosis des poules. Annales de
l'Institut Pasteur, t. XVII, p. 569-580.
10. Anderson. Spotted fever of the Rocky Mountains. Treasury Depart-
ment, Pub. Health and Marine Hospital Service of the U. S. Hygienic
Laboratory Bulletin No. 14.
11. Wilson and Chowning. Report on the investigation of so-called
"Spotted Fever." 1st Biennial Report of the Montana State Board of Health,
15th March 1901 to 30th November 1902.
12. Stiles. Proceedings of the New York Pathological Society. 30th
November 1904.
Abstract in Bull. de l'Inst. Pasteur. Revues et Analyses 30th April 1905.
13. Christy. British Medical Journal, 19th September 1903.
14. Daniels. Reports to the Malaria Committee of the Royal Society
3rd Series.
15. Ross and Milne. Tick Fever. British Medical Journal, 26th Novem-
ber 1904.
16. Dutton and Todd. Mode of Infection in Human Tick Fever. Com-
municated by R. Ross. British Medical Journal, 4th February 1905, p. 280.
17. Browse. A case showing spirilla in the blood simulating Malaria fever.
B. M. J. 11th March 1905.
18. Gibert. L'argas reflexus et son parasitisme chez l'homme. Thèse
Bordeaux, 8vo, 1 plate.
55
19. Hassall. Note on the Chicken Tick, Argas Americanus. Rep. U. S.
Depart. of Agric. Animal Industries, XVI, p. 496.
20. Wellman. Case of relapsing fever with remarks on its occurrence in
the tropics and its relations to Tick Fever. Jour. of Trop. Medicine, 1 April
1905.
21. Lankester. Quarterly Journal of Microscopical Science, September
1904.
22. Dyé. Les parasites des culicides. Arch. Parasitologie, t. IX, 1905.
23. Neumann. Revision de la famille des Ixodidés. Mémoires Soc. Zool.
France, IX, p. 1-44, X, P. 324-420, XII, p. 107-294.
24. Dutton. Report of the Malaria Expedition to Nigeria, 1900. Memoir
IV. Thompson Yate's Reports.
25. Hassel. Note on the Chicken Tick (A. Americanus) Sixteenth Annual
Report of the Bureau of Animal Industries U. S. Depart. of Agriculture,
Washington.
26. Salmon and Stiles. Cattle Ticks of the United States. Seventeenth
Annual Report of the Bureau of Animal Industries, 1900. Washington. Gov-
ernment Printing Office.
27. Lounsbury. The Blue Tick (R. decoloratus. Koch). Report of
the Government Entomologist for the year 1899. Cape of Good Hope.
28. Hart. The tick of the domestic fowl and fowl fever. Bulletin of
Miscellaneous Information. Trinidad III, part 2, April 1899.
29. Lounsbury. Fowl Ticks. Agriculture Journal, Cape Town. Also
Pig Lice, alias Tampans. Agric. Journal. Cape Town, XIV (4).
Explanation of the lettering on Plate I.
Fig. 1. Lateral view of Ornithodoros savignyi (Audouin) (female).
Fig. 2. Dorsal view of same (female).
Fig. 3. Ventral view of same (female).
Fig.2 .
Fig. 3.
S u r v e y o f I n d i a O f f i c e s , C u l c u t t a , J u n e 1 9 0 5 .
PLATE I.
Photogravure.