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partial regression of the salivary glands during mlting or from granule_bearing cells in the accessory organs. The density of these granules in the coxal fluid of newly molted but unfed ticks is mch greater than in the fluid of engorged ticks, in which the granules are more widely dispersed in the greater amount of fluid.

Spiracular Morphology and Function

Argasid spiracles have been described by Robinson and Davidson (1913), Cunliffe (1921), I/Iellanby (1935) and Browning (1951.11). The last two workers paid particular attention to the spiracular struc_ ture and function of Q. moubata.

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As described by Hellanby, the spiracle consists externally of a semicircular cribiform plate inserted into a smooth macula of thickened skin, with a slitlike ostium between these. The thin external layer of the plate is supported by rodlike pedicles. The external layer was stated to be pierced by minute pores opening into the tracheal atrium, which is a tube connected to the ostiu. Muscular attachments of the macula allow opening and closing of the ostium.

If it were true that the external layer is pierced by pores, it would appear that there is no way for the tampan to close off the direct connection between the external air and the internal body tracheae. Since tampans show remarkable ability to withstand desiccation in the laboratory and in nature, Browning (l954A) was led to investigate the spiracle anew. He found that a surface view of the spiracular plate gives the impression of being porous. On examination of transverse sections these “pores” are shown to be expanded distal junctures of branching pillars (pedicels) arising from a basal, underlying layer of sclerotized endocuticle. These pillars support the very thin outer membrane, which is, however, not porous but continuous. The cavity between the basal cuticle and outer membrane and ramifying between the pillars is continuous between the atrium and the spiracle. From surface view the hard maculum can be seen between the inner curves of the crescent of the spiracular plate. The macula encloses a slitlike aperture, or ostium, connecting the atrium of the trachea with the outside air. The argasid spiracular plate functions to provide a pad against which the macula can impinge when depressed

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an thus to form a very efficient seal of the ostium, a necessary
condition for animals so likely to be exposed to desiccation.
€;It is of interest to compare Browning's study with that of

thur (in press) on the spiracle of Ixodes 7.

According to Mellanby (1935), the physiological reaction that governs the opening and closing of the spiracular ostiu is similar to that of insects. Browning (l954B) appears to accept this conclusion. The physiology of spiracular action has been discussed under Environmental Adaptability above.

Haller's Organ

The structure of haller's organ and its su sed value as a phylogenetic indicator has been discussed by E. W. Neumann (1943). Schulze (1941) also described and illustrated ha1ler's organ, which functions as an organ of smell. Incidentally, Zumpt (1949) sumarized his studies on the systematic importance of this structure as follows: Research up to now indicates that haller's organ will have to be considered in the future as having a role in tick systematics and should not be overlooked.

Abnormal Development

Duing examination of about eight thousand laboratory reared specimens of O. moubata, Robinson (l943A) encountered two examples of partial twinning of the posterior area in a third instar nymph and in a fifth instar nymph that subsequently molted to a male and female, each with abnormalities in internal anatomy. These specimens were ormally fertile. Another peculiarly humped third instar nymph normally molted to a male that showed suppression of the postanal region. This male failed to copulate although the enital system was well developed and the sperm normal. Robin. son $19443) also noted many abnormalities of the legs during handling of about ten thousand tampans. Most cases were deficiencies due to partial regeneration of a leg damaged in a previous nymphal instar. Two cases of supernumerary segments of legs were also observed and illustrated. In the same batch a nymph that was much more complete. ly twinned posteriorly than previous examples was observed. This specimen molted to a partially twinned female, mated normally, refused to feed, and deposited a small egg batch (not particularly

unusual for unfed females). Some of these eggs developed into normal ticks but most were not delivered into the arms of gene's organ and therefore did not hatch. In the same paper, Robinson reviewed reports of partial twinning in other tick species. leg anomalies have been reviewed by Campana (1947).

Symbiotes

Tissue cells of many normal insects and ticks harbor living microorganisms that for the most part exert no harmful effects on these cells. In fact, some of them may be distinctly beneficial to the hosts, carrying out their part of a mutually helpful relationship. ZTSteinhaus (1947)J7

In some respects, the relationships between arachnids and their symbiotes are very similar to those between insects and theirs. Among noteworthy differences, however, appear to be the absence of mycetomes in ticks, though some mites have these structures. Furthermore, most tick symbiotes occur in the malpighian tubules and in the ovaries instead of in the alimentary tract, though this may not be true for certain of the rickettsiae. The two families of ticks are similar with respect to symbiotes; in both the same organs are associated with microorganisms. They differ, however, in the manner of ovarial infection. Z_Steinhaus

(19z.7)_7

Intracellular clusters of large masses of typical rickettsiae were discovered in salivary gland acini of 0. moubata by Hertig and Wolbach (1924). Intracellular symbiotes were not found in larvae (?nymphs) of 0. moubata by Cowdry (l925C,l926A,l927), though they were denfinstrated in Ar as ersicus and in Otobius me nini. Other extensive reviews 0 sym 10 es in ticks are thgse of Mudrow (1932) and Jaschke (1933).

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In 0. moubata, unlike ixodid ticks, symbiotes, probably of

a bacterial nature, do not occur in the anterior ends of the malpighian tubes but rather in about one-fifth of the length

of the tubes just posterior of the anterior ends. In this, 0. moubata differs from_A. persicus, in which Jaschke observed intracellular symbiotes in masses as large as five microns in diameter and containing as many as forty individual organisms each.

In 0. moubata and other argasids, symbiotes may migrate from the malpighian tubes to the ovaries and developing eggs, thus differing from ixodids in which they directly invade the first sex cells (Mudrow 1932). This worker sought the explanation of symbiotic bacteria in the realm of ph siologic relations of nu. trition. (See three paragraphs below .

Argasid symbiotes do not appear to be as pleomorphic as those of ixodids and are usually of the rod or coccus type though they are grouped into apparently gelatinous masses or colonies. Rows or chains of granules or filamentous bundles are not seen in these masses. Tick symbiotes have not been artificially cul. tivated although Steinhaus attempted to do so with those from

Ar as rsicus by utilizin fluids and tissues of the chick eméryo. Z gteinhaus (l947iJ7

With reference to the “bactericidal action" in the guts of insects and A. rsicus and O. moubata (Duncan 1926), the reader is referred to subsequent findings in the following series of papers on work done with A. rsicus: Anigstein, Whitney, and Micks (l95OA,B), Whitney,An gste n and Micks (1950), and Micks, Whitney, and Anigstein (1951). The intestinal tract of blood. engorged ticks exhibited significantly higher antibacterial titer than those that had not been fed. Study of animal blood itself revealed erythrocytic enzymatic hydrolysates showing marked in vitro antibacterial effect over a relatively wide spectrum ofmost gram.positive and a few gram.negative organisms. The active principle of the hydrolysate appears to be a peptide amino acid complex, called sanguinin, which, as a powerful enzymatic inhibitor,

represses the growth of several organisms including streptococci, both in vitro and in vivo.

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The role of symbiotes in producing growth.promoting substances in O. moubata (and in bedbugs) has been studied briefly by De Meillon and Coldberg (l947A,B). Feeding nymphal and adult ticks on thiamin.deficient rats resulted in almost doubling the time necessary for completing the tampan's life cycle, increasing the interval between blood meals and mlting, and an additional molt before reaching maturity. Normal growth and reproduction, however, follow feeding on riboflavin.deficient rats (De Meillon, Thorp, and Hardy 1947). The purpose of these experiments, fol.

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