646 Laura Florence 



hollow aculeus or sucker, with which it pierces the skin, and sucks the 

 human blood." He also described the pumplike structure in the head, 

 the peristalsis of the alimentary tract, and the ejection of feces during 

 feeding. Leeuwenhoek (1695) described the hook-bearing part of the pro- 

 boscis and its eversion during feeding, in addition to other characteristic 

 actions associated with the process. 



When fed in captivity, the louse moves its head back and forth close 

 to the surface of the arm and rapidly jerks the antennae up and down. 

 Then, with the head held at right angles to the body, it seems to anchor 

 itself to the skin, probably by the everted teeth of the haustellum. While 

 the stylets are being inserted, the thorax and the abdomen are raised and 

 gently rocked from side to side, and the claws make irregular scratching 

 motions. After the insertion the insect is holding itself in a more or less 

 straight line and at an angle of from 40° to 45° with the arm. As the 

 feeding progresses the body is gradually lowered, until it rests on the arm 

 and with its head forms an oblique angle The act of sucking blood 

 can best be watched in freshly molted specimens. The blood is first seen ' 

 anterior to the eyes in the pumping pharynx, which dilates and contracts 

 with great rapidity, driving its contents into the true pharynx (larynx of 

 Enderlein), whence they disappear under the brain to reappear as a thin 

 red line in the slender esophagus before this passes under the fat cells and 

 muscle of the thorax. Throughout the process a continuous peristalsis 

 passes along the whole alimentary tract, but this has manifestly no con- 

 nection with the drawing of the blood, as suggested by Widmann (1915 a: 

 290). It seems rather to be a means of removing from the posterior 

 region of the stomach and from the intestine the debris of the preceding 

 meal, since it is the habit of the hog louse — at any rate when kept and 

 reared in captivity — to continue feeding until not only all the feces, 

 but also a drop of blood, have been ejected. The latter may be pushed 

 out by the interlocking of the six longitudinal folds of the epithelial lining 

 of the intestine immediately behind the stomach, in order to prevent the 

 escape of the blood from the mesenteron during digestion. At the first 

 feeding after hatching, no blood has been seen to be ejected, and in some 

 cases after the second feeding feces but no blood have been ejected. The 

 average length of a meal is from eight to twelve minutes, but sometimes 

 it lasts from twenty to thirty minutes, and at the close the mouth parts 

 are apparently withdrawn by a short jerk of the head. Occasionally lice 



