G90 Laura Florence 



scattered on the dorsal anterior region of the stomach wall. We have 

 found only two nuclei in any one of these cells, while four or five may be 

 present in each fat cell. Recently Nuttall and Keilin (1921:184) have 

 published the results of their investigation of these cells. By the intracoe- 

 lomic injection of ammonia-carmine, they have demonstrated that the cells 

 in question have, in Pediculus, an excretory-accumulatory function, and so 

 they have named them peri-esophageal nephrocytes. 



THE ALIMENTARY CANAL AND ITS APPENDAGES 



The stomach of the hog louse (Plate LXII, 7) is a simple tubular struc- 

 ture measuring approximately 1.98 millimeters in length. It consists of a 

 wider anterior part 1.38 millimeters long with a diameter of 0.62 millimeter, 

 and a more slender posterior part 0.6 millimeter long with a diameter of 

 0.2 millimeter, and extends from the region of the mesothorax to that of 

 the sixth and seventh abdominal segments, where it bends cephalad on 

 itself for a short distance, receiving the malpighian tubes and passing 

 into the intestine when it again turns caudad. 



The stomach of the adult hog louse differs from that of the man-infesting 

 pediculi in two respects: its anterior end is not divided into two blind 

 pockets, and it does not possess a " Magenscheibe." Strobelt (1882, 

 English trans. 1883:90) found no "Magenscheibe" m Linognatlms viluli 

 (Haematopinus tenuirostris) , while Sikora (1916:62) found one in Pohjplax 

 {Haenuitopinus) spinidosus End. but not in Haemodipsus {Haematopinus) 

 ventricosus End. Sikora describes as present in young specimens of 

 Haematopinus suis a refractive whitish body on the dorsal surface of the 

 abdomen, which in sections shows a structure similar to that of the 

 " Magenscheibe " of man-infesting lice. In the present investigation 

 no such structure has been seen, but the majority of the specimens sec- 

 tioned have been mature lice, and the structure, as Sikora's work suggests, 

 may be present only in the miniature stages. 



That part of the digestive tract lying in the thorax anterior to the 

 entrance of the esophagus differs markedly in its structure from the true 

 digestive mesentcron. That it is to be considered as a terminal enlarge- 

 ment of the esophagus, comparable to the crop of certain insects, is 

 suggested by a number of facts. In gross specimens the musculature of 

 the wall does not resemble that of the true mcsenteron, liecause the 

 circular fibers still lie outermost. At its distal end, just behind the entrance 



