WILLIAMS: BOOPIIILUS ANNULATUS. 
319 
These muscle libers probably function during oviposition, to resist 
the forward thrust of the uterus by compression from the back of 
the abdomen. There are no fibers from the ventral wall directly 
below the uterus and receptaculum seminis but these organs have 
strong longitudinal muscles inserted on thechitinous ridges just inside 
the genital pore. 
Mouthparts and Alimentary Canal. 
The mouthparts are well described by Salmon and Stiles (:02, 
p. 387-392). They are usually spoken of together as the haustellum 
or beak, which is made up of the two mandibles, the mandibular 
sheaths, and the hypostome or radula, with a four-jointed palp on 
either side. PI. 18, fig. 6, is from a fairly perfect section through 
the mouthparts at the level of the third joint of the palpi. 
The hypostome (pi. 18, fig. 6, hyp.) shows six of the eight rows of 
teeth which are upon it; the outer tooth is not sectioned on either 
side. It is due to imperfect sectioning that the epistome or mandi¬ 
bular sheath ( md. sh.) is not continuous around the mandibles, as each 
has its own sheath. The section shows the articulation {art.) of the 
fourth and smallest segment of the palpus with the third segment. 
At the base of the mandibles the two salivary ducts empty into 
the small mouth cavity. One of these ducts is shown in fig. 4 (pi. 
18, sal. dt.). Just in front of the entrance of the salivary ducts we 
may assume that the alimentary canal begins. For though gener¬ 
ally the space between the hypostome and the mandibles is a closed 
cavity for sucking, yet a separation of these organs would locate the 
true mouth between their bases. 
The esophagus passes posteriorly between the sheaths contain¬ 
ing the mandibular muscles as a tube compressed from side to side 
—in cross section a slit. It bends sharply downward in its passage 
and as sharply up again to bore through the center of the ganglionic 
mass (pi. 19, fig. 7, oes .). The esophagus enters the ganglion on its 
antero-ventral margin and leaves it at the postero-dorsal margin. 
Immediately after emerging from the brain the tube, which must 
now be known as the stomach or digestive portion of the alimentary 
canal, enlarges greatly and breaks up into three portions. One por¬ 
tion passes directly toward the right side of the animal, a similar 
portion toward the left side, while the median, larger tube continues 
