A. I). Peacock 
107 
The roof of the sac leaves the floor of the food canal beneath the posterior 
end of the buccal arch anteriorly to the pumping-pharynx. The lumen, seen 
in cross-section (Text-fig. IV, 6, 7 and 8), shows three regions, (1) the wide, 
upper pumping-pharyngeal region, (2) the lower, narrower sac region and 
(3) the still narrower connecting region. The boundaries of the pumping- 
pharyngeal region are a roof made of the arch of the buccal funnel, a floor of 
chitin incomplete in the middle line, and the paired elements of the pumping- 
pharyngeal tube. In cross-section the latter look like round brackets facing 
one another ( ). The boundaries of the sac are two walls largely made up 
of the elements of the sac tubes and a thin floor of chitin. The elements of 
the sac tube in cross-section resemble query marks and face one another S' 
Their dorsal overhanging parts act as guides to the upper stabber. The 
connecting space has thin chitinous walls. The appearance of these structures 
at various points along their length may be followed by comparing the series 
of sections illustrated in Fig. IV, 8-4 with PI. VI, fig. 1. 
The tissues and structures which run forward into the buccal region are 
(<r) the connective tissue outside the floor of the funnel. ( b ) the pumping- 
pharyngeal tube, (c) the sac- tube, and (d) the connective and muscular (?) 
tissues of the wall joining these tubes. Anteriorly to the elements of the sac 
tube remnants of muscular (?) tissue persist. 
Even with the oil-immersion lens it is difficult to recognise the exact 
nature of the tissue of the sac. For about the first third of its length it appears 
to consist of extremely thin chitin surrounded by a fine layer of chitinogenous 
cells, but posteriorly, except in a certain special region of the floor, only a 
thin blue line is shown under the high power. For the first two-thirds of its 
length the cavity of the sac is spacious and contains only the stabbers. 
Posteriorly the sac is almost completely filled owing to the increase in size 
of the stabbers and the presence of their muscles which have a common origin 
at the blind end of the sac. This blind end is supported by a pair of retractor 
muscles whose relationships are discussed later. One part of the floor, roughly 
speaking the middle half, is specialised as a chitinous groove, the sac floor 
groove (PI. VI, fig. 2), the edges of which are thickened and flanged. In cross- 
section (Text-figs. IV, V, 11,12,14) it is shaped like a wide capital U with the tips 
bent outward and thickened. The anterior third is separated from the posterior 
two-thirds by a suture (Harrison). In the posterior quarter of the sac the 
groove disappears. An additional pair of grooves is also present in the floor of 
the sac (Text-fig. IV, 9, 10 and 11). They are laterally placed and reach from 
a short distance behind the anterior portion of the wide sac groove to a short 
distance in front. These lateral floor grooves seem associated with Pawlowsky’s 
glands which open into the sac. The other structures pertaining to the sac 
are Pawlowsky’s glands, sac muscles, and the stabbers with their muscles. 
As the musculature is closely bound up with that of the stabbers it will be 
described after the stabbers. The salivary glands (vide infra) open into the 
sac posteriorly. 
