The Hog Louse 691 



of the esophagus the circular niusclcs 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 Ijoth 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 l)y 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 mescnteron there is 

 a considerable volmiie of blood, and if a smear be made from the contents 

 of such a stomach a large number of intact corpuscles arc 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 kmiina been seen, such as are figured by Sikora 

 (1916:67, PI. Ill, figs. 14, 15) in Pediculiis 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 epithehum, which is much more slender than that of 

 the mesenteron and is covered with a delicate intima, Hes in six longitudinal 

 folds. Three muscle layers are present, but are not readily distinguished 



