464 
HENRY F. NACHTRIEB 
tion and maceration within the pit and thus lead to a lessening 
of the overlapping edges of the ordinary surface cells. This sug- 
gestion occurred to me but recently and I have not had an oppor- 
tunity of testing it. 
Under a medium power, such as a Zeiss D, the epithelium on 
the floor of the pit presents a line of deeply stained nuclei. The 
line of demarcation between these deeply stained nuclei and the 
lighter, less dense nuclei of the cells lining the rest of the pit is 
sharp. It can be readily recognized in figs. 9 and 11, although it 
is not as striking here as it is in the sections. At first glance 
this floor epithelium appears two layered. A careful examination, 
however, convinces one that it is only one cell deep but composed 
of two kinds of cells. The more conspicuous and somewhat more 
abundant cell is a large, relatively clear, columnar cell, less than 
twice as long as it is wide, with a relatively clear cytoplasm and a 
deeply stained spherical nucleus containing several nucleolus- 
like bodies of which three to six may be in view at one focus. 
This is Kistler's ^'supporting cell.'' For reasons that will appear 
later I shall call it the flagellated cell. The other cell extends 
out beyond, and more or less covers the outer ends of the con- 
tiguous flagellated cells. The cytoplasm of this cell appears 
more dense; the nucleus is larger, clearer and usually contains 
but one conspicuous nucleolus-like body. This is Kistler's 
'' sensory cell." I shall call it the cover cell. The two kinds of 
cells are very easily distinguished by their nuclei. In both kinds 
of cells the nucleus lies in the outer portion. In nearly all of the 
preparations the surface of this differentiated epithelium appears 
faintly ragged or fuzzy as if covered by bits of mucus. 
Under a Zeiss 2 mm. apochromatic objective of 1.30 N.A. and 
a number 4 or 6 compensating eye piece the differences just noted 
become more marked and new distinctive features become evi- 
dent in well preserved material stained with Heidenhain's iron 
hematoxylin. The cover cell, shown in detail in fig. 10, is com- 
pressed in the middle so that in optical longitudinal section it 
appears more or less dumbbell-shaped. The nucleus lies in the 
expanded distal portion of the cell and in optical section appears 
triangular because the lower part of it lies in the compressed 
