42 
Argas persicus 
of the denticles is not so uniform as is usually the case in the Ixodid 
ticks, and is subject to a considerable amount of variation. As 
a rule, the tip of the hypostome bears a number of small denticles 
arranged in two or more irregular transverse rows. These are followed 
by some sixteen large denticles, disposed in two files on either half of 
the hypostome, and these again are followed by a series of rows of 
smaller denticles which decrease in size from before backwards and 
vanish completely about the middle of the length of the hypostome. 
The denticles do not as a rule extend to the lateral margins. The 
ventral surface of the hypostome is divided down the centre by a 
longitudinal furrow which gradually becomes obliterated some little 
distance posterior to the denticles. The dorsal surface, on the other 
hand, is deeply concave from side to side, and towards the hinder part 
a deep longitudinal depression, the hypostomal gutter (h.g.), arises, 
which, after running for a short distance backwards along the surface, is 
continued directly into the pharyngeal opening. 
The basal portion of the hypostome is hollow, its cavity being 
continuous with that of the basis capituli behind, and continued forwards 
as a pair of fine canals which run on either side of the median line and 
terminate blindly some little distance behind the extremity. Like the 
chelicerae, the slight differences, exhibited in the form of both palps 
and hypostome, in the two sexes and in the immature stages, have 
no morphological significance. The foregoing descriptions apply more 
particularly to the female. 
The Buccal Cavity. 
Plate V, figs. 16 and 18; Plate VI, fig. 21. 
The intimate relationship which exists between the buccal cavity 
and the capitulum makes it desirable to proceed with its description in 
the present section rather than to postpone it to a subsequent section 
dealing with the alimentary canal. 
An examination of the two sections (fig. 15 and fig. 16 (Plate V)), 
will show that where the base of the hypostome merges into the ventral 
wall of the basis capituli, its lateral margins fuse with the ventro-lateral 
walls of that part of the basis capituli which is continued forwards above 
the mouth to form the cheliceral sheaths. In section (fig. 15) the 
hypostomal margins are still free, but in the following section (fig. 16), 
union has occurred and the space thus enclosed is the buccal cavity. 
