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glands shortly after emergence. In Ixodidae the dermal
glands undergo a complex cycle of growth and degeneration,
but their products appear to add nothing of functional
significance to the substance of the cuticle.'

Lees' important contributions indicate why 0. moubata is capable of surviving in the dry niches in which domestic popu lations occur. However, we still lack data on the actual rel. ative humidity of these niches in nature. We know only that the tampan can withstand these conditions in laboratory investiga tions. And it should be stressed that we still know nothing about preferences and critical levels of temperature and humidity among burrow_haunting populations. The Bahr El Ghazal collections, from warthog burrows in the "Nile sponge area", especially excites curiosity in this respect.

Laboratory studies on the optimum temperature and humidity conditions under which 0. moubata survives have resulted in wide ly differing data and conclusions. The reports in question are those of Cunliffe (1921) and Brett (1939) together with those of Robinson (1942C) and others already reviewed in the section on the life cycle of 0. moubata.

Cunliffe found that a saturated atmosphere has no inhibitory influence on molting but is decidedly unfavorable for vitality (only one specimen passed the third nymphal stage under these conditions). Even under "medium conditions of humidity, mortality is high, but under "dry conditions, 66% of the nymphs complete metamorphosis and the rate of development is increased. High temperature increases the number of eggs laid but decreases fertility, longevity, and time required for metamorphosis,

Brett, on the other hand, found that (at 25°C.) higher rel ative humidity (up to 80%) was more favorable for survival of eggs, larvae, and first instar nymphs (the only stages and in stars tested) though a proportion of all eggs were able to develop at any "low humidity normally met with in nature. He also found that the first nymphal instar is much more resistant to desiccation than larval and egg stages. The apparent inconsisto ency between Brett's findings and the known fact that domesticated populations of 0. moubata are chiefly inhabitants of drier areas

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Figure 56 ORNIT HODOROS MOUBAT A INTERNAL ORGANS [ After Burgdorfer (1951), with permission of

the editor of ACTA TROPICA 7

PLATE XIX

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Midgut
Salivary gland

Ovary
Uterus Oviduct
Central ganglion

Malpighian
Oesophagus

tubule
Pharynx

Rectum
Accessory
dlandFilter chamber

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Host blood cells

58
Figures 57 and 58, , Unengorged and Engorging

Spirochetes of African tick-borne relapsing fever, Borrelia duttonii, are illustrated, as short wavy lines, in the positions they occupy in the tick's body. Note their escape routes from the tick's body and into the host's body while the tick is feeding.

ORNITHOD OR OS MOUBATA DIAGRAMMATIC SAGITTAL VIEW
[ After Burgdorfer (1951), with permission of

the editor of ACTÁ TROPICA

PLATE XX

- 158

is explained on the basis of Williams (1923,1924A,B) and Buxton's (1932, 1933) exposition of the comparatively high humidity in sand, cracks of walls, and soil in areas that are otherwise dry. Brett's discussion and the comparison of his findings with those of Cun liffe and of other workers, especially those of Robinson (19420) discussed on p. 137, which corroborate those of Brett, should be studied for their practical importance by anyone concerned with 0. moubata. Since only careful and thorough research in the field as well as in the laboratory can conclusively settle the matter, a more complete discussion of this question is hardly in order here.

Structure and Function

Introduction

No thorough studies of the internal anatomy and histology of 0. moubata have been undertaken. What has been done on certain aspects of these subjects is reviewed in the following paragraphs. On the whole, workers have been content to accept Christophers' (1906) careful though still somewhat general description of the internal anatomy of 0. savignyi as also applicable to 0. moubata. Recently, Burgdorfer (1951) has provided a short account of the internal anatomy of 0. moubata and some of his excellent illustra tions are reproduced (Figures 56 to 58). However, 0. moubata deserves more specialized attention than it has thus far been accorded. These two species differ in habits, habitats, distri. bution, and receptivity to pathogenic organisms. It may be expected, therefore, that under their leathery shells, which also differ, significant anatomical and physiological differences remain to be demonstrated.

Internal Anatomy

The general features of the internal anatomy of these two species are similar and Christophers' (loc. cit.) description of a dissection of o. savignyi as presented below, applies equally well to 0. moubata Twith known differences noted):

Over the whole dorsum lies a fine membranous ex pansion of tracheae and trabeculae of the fat body. Lying in this, in the median line, is the delicate tubular heart. Posteriorly, at about the junction of

the middle with the posterior third of the body, this is considerably dilated. Stripping off the expansion, the main mass of the viscera, consisting largely of the large dark red blood sacs of the alimentary canal, are exposed. By carefully unravelling these, the arrangement of long diverticula, described later, can be made out. Lying upon the diverticula in the posterior portion of the body is the ovary, studded with developing ova. Upon either side of the ovary are the coiled oviducts, and in the middle line is the large conspicuous bilobed spermatheca (uterus). In almost every region of the body a portion of the thin coiled malpighian tubules will be found. Behind the sperma theca is an opaque white organ, having very thin saccular walls and filled with characteristic white secretion from the malpighian tubules. This is the rectum (rectal ampulla), which in ticks serves as an excretory bladder. By displacing the diverticula from the extreme anterior portion of the body a bilobed glandular organ, the cephalic gland (gene's organ) is displayed. Further back, the bulbous ends of the Cheliceres with radiating muscular fibres are seen, Around them will be noticed the ringlike chitinous fold at the base of the rostrum. By displacing to one side the whole of the anterior and lateral diverticula, a member of further structures are apparent. Passing in from the stigmatic (spiracular) openings is a leash of tracheal branches, of which the large anterior ventral trachea is the most conspicuous. Lying upon the origin of the first and second legs is the large racemose gland which functions as the salivary gland in ticks. Lifting this gland by its posterior extremity, which lies on the anterior ventral trachea, and tracing it forward, the short salivary duct will be apparent entering the ringlike fold of chitin, already mentioned, immediately beneath the cheliceres. Lying partly under the salivary gland, and partly internal to this structure is (the large, saccular coxal organ) conspicuous from the number of tracheae which supply it.

""By careful examination, the delicate, colorless esophagus can be made out entering the lower surface of the large median blood sac of the alimentary canal, whilst lying behind the spermatheca is the fine hairlike termination of the sac in the rectum, To the reco

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