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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 ar. rangement 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

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 pumping 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 es. sentially 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 O. coriaceus, and Sen 1934,1935 for o. tho Lozani) 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 haemo coele. The hypostome is concave dorsally; ventrally it bears rows of distinctive retrograde denticles. The chelicerae distally each bear a small, triangular, articulated digit, at tached 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. wmouth") lies between the dorsal chelicerae and the ventral hypostome; proximally 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.
F.

HD.
M.C.PH.

Figure 59. Longitudinal vertical section, diagrammatic

[After Bertram (1939) 7

ORNITHODOROS MOUBATA CAPITULUM

PLATE XXI

. 163.

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When preparing to engorge, the tick inserts the chelicerae and 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

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