Gr. H. F. Nuttall and D. Keilin 185 
filament which may perhaps be a duct has been noted passing upward with 
the salivary duct/’ 
These cells were also observed by Muller (1915, p. 15), who described them 
in a few lines in his chapter on the fat body. The only interesting statement 
he makes is that these cells owing to their size, shape and occurrence in 
groups, recall the pericardial cells of other insects but differ therefrom, how¬ 
ever, in respect to their position. 
Sikora (1916, pp. 57-58) subsequently gave a good description, calling 
them “large celled glands” (“Grosszellige Drusen”). She studied them in 
sections and found that there were 46-56 cells (“ Drusen ”) on each side of 
the oesophagus, although she stated that the number may be much smaller 
because it was possible that she counted some of the cells twice over. She 
found that the cells are binucleate and frequently show cleft-like spaces 
(“spaltformige Saftraume (?)”) between their nuclei. The cells are oval and 
often prolonged into a filament; other very fine filaments connect them 
to each other and serve to attach them to the surrounding organs. Sikora 
found no efferent canal connected with the cells and supposed that their 
function consists in taking up certain substances from the perivisceral fluid, 
either storing, transforming, or eliminating them again into the perivisceral 
fluid. She compares these cells to the binucleate cells found by her in the 
vicinity of the heart in transverse sections of Haematopinus eurysternus. 
The foregoing paragraphs afford a summary of all that has been pub¬ 
lished hitherto regarding the structure of these cells. 
In the course of our studies on Pediculus, we have been able to confirm 
the statements of the above-cited authors regarding the structure of the cells 
in question. We have, however, found cells of a similar structure in other 
parts of the body of the louse and have succeeded in determining the hitherto 
unknown function of all these elements. 
For reasons to be given presently, we shall henceforth refer to these 
binucleate (at times trinucleate) elements as Nephrocytes. The elements re¬ 
ferred to by the above-cited authors will be termed by us peri-oesophageal 
nephrocytes (ventral, in clusters), the others will be termed disseminated 
nephrocytes (dorsal). 
Peri-oesophageal Nephrocytes in Pediculus. 
The number of nephrocytes belonging to this category is certainly inferior to 
what Sikora supposed, for we have been unable to count more than 16 to 20 
on each side of the oesophagus. In sections the nephrocytes appear as large 
binucleate or at times trinucleate cells possessing very granular protoplasm 
(Fig. 1). The cleft-like spaces of Sikora appear to be artefacts due to fixation, 
since they are not visible in the living tissue. The nuclei are vesicular, and, like 
the nuclei in the other tissues of the louse, they are very poor in chromatin. 
The chromatin is reduced to a few granules, the rest of the nucleus being clear. 
