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gans while the tick is yet feeding. Rectal discharge is very slight. These two methods of excretion are discussed in separate sections below.

Digestion in O. moubata apparently is much like that in Q. savignyi,as described By Christophers, abstracted below.

Twenty-fou hours after a meal the greatly distended diverticula contain a soft coagulum from.which a considerable amount of fluid blood may drain. Blood corpuscles are apparently unchanged. Scattered through the fluid are numbers of intensely black, globular granules masuring from 5u to .5u or less in diameter. In sections these granules are collected especially at the periphery of the (fresh) blood, but they are also present in large numbers scattered throughout the mass. The black granules are derived from a previous meal, and there is therefore a considerable degree of mixture between the new blood and the contents of the diverticula prior to the meal.

Diverticula examned at some considerable time after digestion show a number of reddish granules lying in the still partially fluid blood. These are free from attachments and when washed out fall to the bottom of the dish or among the viscera. Each is an entire cell containing a well-marked nucleus. Films of the sac contents made twenty-four hours after a blood meal show cells derived from the epithelium of the sac in addition to the host's leucocytes. Many of these are evidently the smaller undistended cells, previously noted as lying near the basement membrane, now detached in preparation of the specimen. They contain a large circular or oval nucleus and finely reticular or partially vacuolated protoplasm. Similar cells, but larger and with portions of the vacuolated protoplasm stored with black granules, are also seen. In addition to these cells of the sac epithelium, there are other large, dark staining, circular cells with rather small nucleus. Their substance is markedly vacuolated and crowded with matter that they evidently have engulfed, blood corpuscles, black granules, chromatin fragments, etc. In section specimens made even six hours after the ingestion of blood, they appear lying apparently in isolated positions far removed from the sac walls. These probably function as wandering digestive cells. Their relation to the epithelium of the sac is not clear. As digestion ad

vances they become more and more replete with material and in. crease in size until readily visible to the naked eye as red granules already noted. In early stages of digestion, cells packed with chromatin bodies and superficially resembling macro. phages, the nature of which is not clear, may be seen.

Although a prominent part in digestion is taken by the free cells just alluded to, epithelium lining the diverticula also takes an active part in the process. The swollen and vacuolated portion of the large projecting cells is crowded with products of digestion very much as is that of the free cells. Smaller cells lying nearer the basement membrane are also, as a rule, packed with fine black granules, though they rarely contain the large granules seen in the other cells.

The intensely black and opaque globules are highly characteristic of digestion in the tick and undoubtedly represent the ultimate condition to which blood remaining in the gut is reduced by the digestive process. These globules probably represent only the portion of food not assimilable, for in Ornithodoros ticks, -which may be kept alive for long periods without food, the diver. ticula contain, after some weeks, an inky black material consist. ing entirely of these granules.

As diverticula contents are digested, the muscle fibres, which in the fully distended organ slightly indent the suface, sink more and more into the body of the viscus. The wall between the fibres becomes ballooned and eventually forms flasklike pock_ ets with only a narrow opening connecting with the lumen. The epithelium is, as a rule, present in the pockets, though it is generally more noticeable on the ridges formed by the contracted muscular fibres. Remains of ingested blood, in the form of black granules, are present both in the pockets and in the lumen. Ticks examined months after a meal still have the diverticula loaded with the black material.

Waste matter is not passed into the rectum and an remnant of foo not absorbed must remain in the_divert1c§Ia un¥iI death

6? the £IER. The neth5d_by wh1cH_§b§5rpt1on takes p[ace has not YEeK_§scertained. Black pigment is not detected in the tissue cells or in the body cavity. Note that excess fluid in the blood is excreted by the coxal organ during and following feeding so that a large amount of blood can be rapidly ingested; this is elucidated in the section on the coxal organ below.

[graphic]

Wigglesworth (1943) confirmed that in O. moubata, blood (haemoglobin) is absorbed by swollen epithelial cells of the wall of the large stomach ad its diverticula. In these cells, which detach and remain free in the luen, blood pigment is converted into black globules that are ultimately discharged into the gut cavity. Similar dark granules are dispersed through smaller cells of the gut wall, but no black pigment can be seen in other tissues or in the body cavity. The haemoglobin is digested more or less to protohaematin and is demonstrable in the tick's haemo_ lymph probably as alkaline haematin. The gut contents are reddish brown with black haematin deposits. No free iron can be detected in the gut lumen or cells, or in other tissues, and no nephrocytes containing haemoglobin derivatives can be found.

The type of host from which Q. moubata draws a blood meal may be identified by the precipitin test more than six months follow; ing feeding (laboratory studies at 2090. and eighty percent relative humidity) (Weitz and Buton 1953), or even for twelve months (fowl blood meal, kept at 30°C., ticks also fed on mouse) (Gozony, Hindle, and Ross 1914).

Rectal Excretion

As stated above, 0. moubata has no passage between the small intestine and the rectal ampulla, and defecation does not occur. Excretion of water (“urination”) from the malpighian tubules takes place only after the first nymphal stage has been reached and a blood meal has been absorbed; this excretion is viscous and dries within a few hours. In the weeks following the first excretion only a slight amount of water is irregularly excreted (but can be produced through various stimli). This pattern is similar in each developmental stage after the larva.

Variations in tick excretion and a comparison of this function according to species, morphology, number of hosts, size, duration of development, quantity of blood ingested, and transmission of disease organisms to vertebrate hosts have been analyzed by Enigk and Grittner (1952),

Coxal Organ Morphology and Function*

Inasmuch as the volume of the blood meal is from two to six times the tick's original body weight and engorgement is usually completed in about half an hour, the tick must have a means of reducing the total intake volume and of preserving the internal medium while feeding. For this purpose coxal organs function as ionic (chloride) regulators and for ultrarapid excretion of a large volume of water during ingestion of blood. Coxal dis. charge, which commences about fifteen minutes after the tick has begun to feed, continues till completion of the meal and inter. mittently for about an hour afterwards. (See also Lavoipierre and Rick 1955).

Malpighian tubules do not function until about an hour after feeding is completed, and the amount of water they excrete is limited.

Chloride re ulation. About half the ingested water is ex. creted in cox ui . The mean haemolymph chloride concentration before feeding is 1.0% and after feeding 0.96% Neill; that of coxal fluid is o.sq% NaCl. These values are similar to those determined by Bone (1943).

Mar holo of coxal or ans. The flaskshaped coxal organs, which elaborate ¥Eé‘BGIi o uid, consist of an outer filtration

chamber with an inner tubule system leading to the external open. ing and of a small organ with glandular structure, the so.called

accessory gland. The filtration chamber, which communicates with the tubules of only one point, is highly folded into an elaborate series of pockets and fingers that closely invest the tubules;

[graphic]

*Chiefly from Lees (19468). See other remarks in section on life cycle. It should also be mentioned, for practical gignificance in relation to disease, that Lees found that O. delanoei acinus and O.

parkeri have coxal organs differing from those of O. moubata, and_

that in these species coxal fluid is liberated only after cessation of ingestion. It should also be noted that what lees and others have called “coxal gland“ is rather a coxal organ (Bugdorfer 1951) because it excretes fluid rather than secreting fluid, and the filter chamber histologically has no glandular structure.

numerous small muscle fibres inserted in these pockets pass out. wards from the organ to attachments on the body wall. The histol_ ogy of the two regions is entirely different. The filtration membrane is only one or two microns thick and its cellular origin is much obscued. The tubule walls, from five to thirty microns thick, are composed of cells with a dense, deep1y.staining cyto_ plasm and are richly supplied with tracheae.

Function. The production of coxal fluid is under muscular control. It is believed that contraction of coxal organ muscles enlarges the filtration chamber and sets up a sufficient pessure difference across the membrane to initiate filtration into the organ. In subsequent passage of fluid down the tubules, threshold substances such as chloride are reabsorbed. That the coxal fluid is primarily an ultrafiltrate of the haemolymph is suggested by (a) the rapid passage of dyes and even haemoglobin into coxal fluid after injection into the haemolymph, and (b) the very high rate of fluid liberation. Serum albumin sometimes passes into coxal fluid

after injection, but casein (and normal haemolymph proteins) are fully retained (Lees' summary).

Bone (1943) proposed somewhat different explanations concerning coxal organ function. Lees further indicates that Patton and Evans‘ (1929) opinions regarding the functions of the coxal organs are in.

cqrrect. An earlier work on the same subject is that of von Kunssberg (1911).

The small accessory coxal glands have an unknown function. Rapid engorgement in argasid ticks is allowed by passive cuticular stretching. In ixodid ticks new cuticle is produced to allow for volume of intake and engorgement is much ore slowly accomplished.

When specimens of 0. moubata and other argasid ticks that possess coxal organs are warmed or irritated they exude from these organs a clear fluid. This may possibly serve in part as a defen. sive mechanism although the actual reason remains to be determined. Coxal organ discharge has been observed and reported, highly in. accurately, by Remy (l922A, and for Ar as reflexus, 1921 and 1922B), who believed the exudate to be haemolymph containing haemocytes. lees (19468) has shown that these structures are actually small, globular clusters of refractive granules, possibly derived from

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