L. E. Robinson and J. Davidson 
238 
Pis. XIV and XV and PI. XVI, fig. 5, st .)—which occupies the central 
part of the body cavity, extending from the dorsal surface of the brain 
in front, to a point a short distance anterior to the level of the anus. 
In the adult stage, the stomach overlies and, together with its coecal 
appendages, almost entirely conceals the genital organs from the dorsal 
aspect. At its anterior and posterior extremities, the stomach is 
bifurcated, giving ri.se to four great lobes which occupy respectively the 
four quarters of the body. For purposes of distinction, these coecal 
lobes may be termed cmtero-lateral (right and left), and postero-lateral 
(right and left). The deep notch which separates the antero-lateral 
and postero-lateral coecal lobes of each side runs obliquely forwards 
from the margin of the body to the anterior end of the stomach (see 
PL XIV), and through this notch certain coxal and other muscles pass 
upwards to their places of insertion into the dorsal cuticle. Through 
this great notch also pass the great postero-dorsal tracheal trunk and the 
Malpighian tubules after their dorsal course over the postero-lateral coecal 
lobe. Two other deep notches are worthy of mention. The first of these is 
that which divides the postero-lateral lobe into two nearly equal portions. 
This notch contains the postero-accessory dorso-ventral muscles, and 
through it the Malpighian tubules reach the dorsal surface of the 
alimentary canal. The second notch is the median unpaired division 
between the right and left postero-lateral coeca, through which pass 
the postero-median dorso-ventral muscle columns. The antero-lateral 
coecal lobe is generally divided by deep marginal notches into two or 
more parts, but these notches are not so constant in their arrangement 
as those described above. They afford a means of passage for the first 
three pairs of abductor muscles of the coxae, the fourth pair passing 
with the adductor muscles of the coxae through the notch between the 
antero-lateral and postero-lateral coecal lobes. Further reference to 
these muscles will be made in a subsequent part of this paper dealing 
with the musculature. The ultimate terminations of the alimentary 
coeca form a series of sacculated pouches, which reach almost to the 
peripheiy of the body, the shallower notches which divide these 
marginal pouches accommodating the marginal dorso-ventral muscles. 
The general appearance of the stomach depends upon the state of 
engorgement of the tick. The empty stomach, with its appendages, is 
pale in colour, but assumes a deep purple-red hue after engorgement, 
which, as digestion proceeds, changes to chocolate and then to dark 
brown. In old specimens in which digestion is complete, the entire 
organ becomes collapsed and flattened and presents a dirty greyish-black 
Parasitology vi 16 
