230 
Argas persicus 
anterior end, where the direction of its lumen turns upwards and for¬ 
wards to enter the buccal cavity. The walls of the pharynx are composed 
of a hypodermal layer and a stout chitinous lining, the latter representing 
the cuticle, here specially developed, which is common to the whole 
cour.se of the fore-gut. 
The real nature of the organ becomes apparent from the examination 
of its transverse section (see Text-figs. 2 and 3). It is then seen that 
the walls are tlirown into a number of sharp regularly-disposed longi¬ 
tudinal folds, arranged in such a manner as to give it a tri-radiate 
cross-section. Two of the radii form the dorsal part, and a single 
median ventral radius completes the figure. The extremity of each 
radius is divided by a deep infolding of the pharyngeal wall, thus 
Lumen 
of pharynx 
Dorsal 
dilator muscles 
Constrictor 
muscles 
Peripharyngeal 
Lateral 
dilator muscles 
Fig. 2. Argas persicus i. Transverse section through middle portion of pharynx. 
As the lateral dilator muscles pass obliquely backwards, their attachments to the 
wall of the basis capituli do not appear in the section, x 130 diam. 
giving the section of the pharynx a form which may be compared 
to a Maltese cross with three arms. 
From the walls of the pharynx, regular series of muscle-bands radiate 
on all three sides of the organ, the muscles of the dorsal surfaces being 
attached at their distal extremities to the under surface of the sub- 
cheliceral plate, and the lateral muscles to the wall of the basis capituli. 
In addition to these, a second series of smaller muscle bands are seen to 
connect the extremities of each of the radii with one another, and also 
the bifurcated extremities of each radius. These muscle bands, which 
thus form a complete ring surrounding the entire circumference of the 
pharynx, alternate in a perfectly regular manner with the above- 
mentioned radiating bands. 
