690 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 malnighian 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.” Strdbelt (1882, 
English trans. 1883:90) found no ‘‘ Magenscheibe”’ in Linognathus vituli 
(Haematopinus tenuirostris), while Sikora (1916:62) found one in Polyplax 
(Haematopinus) spinulosus 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 immature 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 mesenteron. That it is to be considered as a terminal enlarge- 
ment of the escphagus, 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 mesenteron, because the 
circular fibers still lie outermost. At its distal end, just behind the entrance 
