THE Hoa Louse 691 
of the esophagus the circular muscles become emphasized as a narrow 
band and the longitudinal fibers pass out from under them, forming, 
on the surface of the true stomach, with the underlying circular muscles 
an open-meshed network. A study of sections has revealed no trace 
of an esophageal valve, either where the slender esophagus passes into 
the enlarged part or where the abrupt transition to a digestive epithelium 
takes place, and the structure of the wall is identical in both slender and 
enlarged parts. A similar abrupt transition from the esophagus to the 
mid-intestine without the intervention of a valve or a sphincter has been 
described in the bedbug, by Cragg (1915:709). It consists of a delicate 
muscular coat and a layer of much-flattened epithelial cells lined by a 
fine chitinous intima. In the region of the above-mentioned circular 
muscle band there is an abrupt transition to the digestive part of the 
stomach, which is lined with a layer of secretory epithelial cells. In lice 
dissected some hours after feeding, the thoracic enlargement is frequently 
found empty; while in the anterior part of the true mesenteron there is 
a considerable volume of blood, and if a smear be made from the contents 
of such a stomach a large number of intact corpuscles are found. Also, 
where digestion is taking place the active epithelial cells shine through 
the stomach wall as light spots among the blood, a condition never seen 
in the wall of the anterior dilatation. 
At the junction of the stomach and the intestine, four malpighian 
tubes are given off. They measure approximately 6.3 millimeters in 
length and 0.25 millimeter in diameter, and are about two and a quarter 
times as long as the combined length of the stomach and intestine. They 
first pass backward along the sides of the intestine, and then forward 
to the anterior end of the abdomen, where they turn again caudad ter- 
minating finally in the region of the last two abdominal segments. In 
structure they show no unusual features, and in no sections have secondary 
invaginations of their lumina been seen, such as are figured by Sikora 
(1916:67, Pl. III, figs. 14, 15) in Pediculus vestimenti. 
Posterior to the malpighian tubes lies the small intestine. It has an 
approximate length of 0.43 millimeter and diameter of 0.2 millimeter. 
When empty its epithelium, which is much more slender than that of 
the mesenteron and is covered with a delicate intima, lies in six longitudinal 
folds. Three muscle layers are present, but are not readily distinguished 
