694 LAuRA FLORENCE 
and in accordance with the mode of life of the insect it appears to be 
always in a state of activity. In the study of the epithelium many series 
of sections of the alimentary canal have been made, at intervals of from 
half an hour and one hour after the time of feeding up to twelve hours, 
by which time the stomach in captive specimens appeared to be empty of 
blood. Sections have also been made of lice starved to the point of death. 
The epithelial celis vary in outline according to their state of activity. In 
the resting stage (Plate LXIII, 1) they are flattened and extend farthest 
into the lumen in the region of their nuclei. During absorption the 
individual ceils expand until they appear cuboidal, and during secretion 
the free ends of the cells, where the ball of secretion accumulates, become 
subcircular. These secreting cells show great variation in the degree 
to which they extend into the lumen. They may remain attached to 
the basement membrane by a broad base, or they may be greatly atten- 
uated and apparently attached to the membrane by a very narrow base, 
and in sections blood is seen extending between the individual cells 
(Plate LXIII, 1). In no case has a definite cell wall been found between 
any two cells, and the whole appearance suggests a syncytium; but further 
proof would be necessary before the acceptance of this view. Each 
cell has a large oval nucleus with a subcentral nucleolus surrounded by 
irregularly scattered chromatin granules. There is considerable variation 
in the position of the nucleus in the cell, and this, in addition to the 
irregularity of the cells, gives the effect of a several-layered epithelium 
(Plate XLITI, 1 and 2). In most cases the nucleus is seen lying in the 
cytoplasm immediately behind or to one side of the secretion products, and 
on their excretion remains intact, but in a few cases the nucleus has been 
seen to be carried along with the secretion (Plate LXIII, 2). In the latter 
case the death of the cell must follow, and the question of its replacement 
arises. In many insects a regular destruction of the epithelium takes 
place and new cells are formed from regenerative centers, or nidi; but no 
such structures are present in the hog louse, nor has Sikora (1916:65) 
found them in Pediculus vestimenti. Nuclear division has not been seen 
taking place in the epithelium, but just within the basement membrane 
at the base of and between some of the epithelial cells lie single, very small 
nuclei, each hardly more than a nucleolus, definitely surrounded by a 
small amount of protoplasm; and these may be the source of the new 
epithelial cells. A similar condition was described by Van Gehuchten 
