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tum can be traced the attached end of the two extremely
long malpighian tubules. To display the esophagus in
its passage from the pumping organ to the alimentary sac
it is necessary to tear away the dense mass of muscle
from which it will be seen to emerge. By seizing the
muscular mass boldly in the forceps, the unattached
entosternum surrounded with muscle will come away,
exposing the central ganglion, perforated by the eso.
phagus. By seizing the bulbous ends of the cheliceres
they may be drawn from their sheaths. Lying beneath
them is the horizontal entosclerite of the head. Beneath
this, again, is a dense mass of muscle within which lies
the chitinous prmping pharynx.

"In the male, in the position of the ovary in the
female, there is a delicate tube abundantly supplied
with trachea. On either side this is continuous with
a coiled duct much resembling the oviduct in the female.
In the middle line, much in the position of the sperma
theca in the female, is a curious lobular organ, the
white gland "(that) is probably concerned in the
elaboration of spermatophores.

Following this, Christophers (loc. cit.) presented a more complete account of each structure and a generalized description of the digestive process in 0. savignyi. This should be consulted by anyone interested in the internal anatomy and function of either species. Sections of Christophers' study dealing with the digestive system are abstracted below because of their relation to the ingestion, development, and passage of pathogenic spirochetes and other organisms, but it is advisable first to mention more recent studies of feeding organs and mechanism.

Feeding and Digestive Organs

The capitulum and related organs of 0. moubata have been studied in considerable detail by Bertram (1939) and reviewed in relation to these organs throughout the Arachnida by Snodgrass (1948). Both papers, which also review previous studies and concepts, deserve careful study. Because of their specialized nature, a short abstract of either of these two studies hardly

does it justice, Snodgrass observes that the exact method by which a tick bites perhaps needs more study than has been given to it".

According to Bertram, the capitulum of 0. moubata is essentially similar to that of other argasid ticks (see Christophers 1906 for 0. savignyi, Robinson and Davidson 1913A,B,1914 for A. persicus, True 1932 for 0. coriaceus, and Sen 1934,1935 for 0. tholozani) although certain modifications in the eyeless tampan are either absent in other species or have not been adequately described. Bertram also differs widely from Sen in explanation of specific structures and fundamental interpretations.

The capitulum (Figures 59 and 60), situated in a depression (camerostome) of the anteroventral body surface, consists of a median hypostome flanked by a pair of four-segmented palpi and a pair of long, shaftlike chelicerae arising from a conical prolongation of the basis capituli. Each of these hollow appendages contains haemocoele. The hypostome is concave dorsally; ventrally it bears rows of distinctive retrograde denticles. The chelicerae distally each bear a small, triangular, articulated digit, attached by flexor and extensor muscles, with laterally directed denticles. These digits make the initial incision in the skin, A triple sheath arrangement of no little complexity encases the chelicerae proximally. The buccal canal (i.e. "mouth) lies between the dorsal chelicerae and the ventral hypostome; proximal. ly it is much compressed. The size of this canal is somewhat in creased by the medial emargination of the closely appressed che. liceral sheaths and by the dorsal groove ("gutter) of the hypostome which forms a food conduit. Extending into the center of the buccal canal is a hollow, "tongue-like process", the basal fusion of which with the hypostome forms a dorsal, blindly-ending pouch, the buccal cavity, into which a salivary duct issues at each posterolateral angle. The buccal canal opens directly into the pharynx, as one might logically assume it should, except that previous workers have found that in other ticks the basal fusion of the hypostome, palpi, and dorsal conical prolongation of the basis capituli causes the pharynx to open into the floor of the buccal cavity.

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B.C.
B.CH.
BUC.CAN.
BUC.CAV.
CAM.
CH.
C.SH.
D.CH.
D.C.P.

basis capituli

M.D.HG. expanded base of chelicera M.D.PH. buccal canal

0.PH. buccal cavity

P.C.C. camerostome chelicera

PH. cone sheath

S.CH. digit of chelicera

S.CH. dorsal conical prolongation SUB.CH.P. of basis capituli

TG. salivary duct

TH. flange of chelicera hypostome hood

V.R. constrictor muscles of pharynx

V.S.

dilator of hypostomal gutter dilator muscles of pharynx pharyngeal orifice posterior part of closed chamber pharynx outer sheath inner sheath subcheliceral plate tongue_like process transverse bar formed by fusion of lateral thickenings of tonguelike process ventral rod of tongue like process ventral scutum in cavity of closed chamber

D.SAL. ?. H.

44.C.PH.

Figure 59. Longitudinal vertical section, diagrammatic

[ After Bertram (1939) 7

ORNITHODOROS MOUBATA CAPITULUM

PLATE XXI

. 163

19

09

Figures 60 and 61, dorsal and ventral views

ORNITHOD OROS MOUBATA CAPITULIM

PLATE XXII

When preparing to engorge, the tick inserts the chelicerae ind hypostome (not the palpi) into the host skin as far as the dorsal conical prolongation of the basis capituli.

During feeding (according to Bertram), the dilatation and constriction of the pharynx by certain muscles cause the fluid contents of a closed chamber just posterior of the tonguelike process to be forced into and sucked out of this process through a vertical septum. Furthermore, relaxation of hypostomal muscles obliterates the hypostomal gutter as the dilated pharynx constricts to force ingested blood into the esophagus. The effect of this swelling of the tonguelike process and closure of the hypostomal

furrow is to prevent the spilling back into the host's wound of any blood already in the pharynx. The tonguelike process also appears to play an essential part in the mechanism of ejection of salivary fluid into the blood as it is being ingested. Since the salivary fluid is discharged into the distal region of the buccal canal, it is assumed to reach the wound in the host (and thus might transmit disease causing organisms contained in it).

As stated above, Bertram's study has considerable practical value, but must be read in its entirety to be fully appreciated. It should be noted that Snodgrass (1948) refers to the tonguelike process as the labrum in his noncommittal review of Bertram's findings and conclusions.

Alimentary canal: We now return to Christophers (1906) study of O. Savignyi, and it is interesting to note that he found the pharynx to open into the floor of the "mouth" (buccal canal) in contrast to Bertram's observation on 0. moubata, mentioned above. At any rate, the pharynx leads to a narrow, straight esophagus. The latter, after perforating the central ganglion, enters the enormous saccular midgut, which, with its diverticula, forms the great bulk of body contents. Posteriorly, an extremely fine canal, which appears to be a functionless rudiment, joins the midgut with the rectal ampulla (but in o. moubata even this is absent and the alimentary canal ends in a completely closed sac separated from the rectal ampulla) (see below).

Esophagus and proventricular fold. The esophagus, a short, straight tube perforating the central ganglion in its course from pharynx to alimentary sac, is lined with a layer of clear columnar cells with small nuclei. The irregular outlines of these cells are mutually adapted to one another in a dovetailing arrangement. At the juncture of the esophagus and large blood sac there is a small solid organ. This organ, in section, consists of a thick fold of epithelium of the same general character as that in the esophagus but of more columnar and less irregular cells. In the fold are some thick circular bands of muscular tissue and outside are longitudinal fibers passing from the esophagus to the gut. The epithelium of the fold passes imperceptibly into that of the esophagus, but ends abruptly on reaching the wall of the alimentary sac. The organ is very similar to, though

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