PRIMITIVE PORES OF POLYODON SPATHULA 465 
region of the cell. It appears clear and has a loose, large-meshed 
network in which there usually is one large nucleolus-like body. 
The cytoplasm appears homogeneous, sometimes suggesting 
longitudinal striation in the basal and compressed region of the 
cell. The base or proximal end is always expanded and in close 
contact with the basement membrane. In most of my sections 
the free surface appears more or less fuzzy. This appearance 
is due to bits of mucus adhering to very short and variable 
pseudopodia. My reasons for not considering these processes 
permanent cilia or sensor}- hairs are: 1, They are indefinite and 
variable in shape and length; 2, There are no basal bodies in con- 
nection with them; 3, In many preparations the surface of the 
cover cell is in intimate connection with the mucus in the pit. 
In sections showing masses of mucus in the pits the strands of 
mucus are frequently so intimately related to the surface of the 
cover cell that it is impossible to determine where the cell sub 
stance ends and the mucus begins. In such preparations the 
free surface of the cover cell is uneven and may have relatively 
wide projections continued uninterruptedly into masses or 
shreds of mucus far from the surface of the cell. In sections of 
material hardened in platino-aceto-osmic and stained with iron 
hematoxylin the mucus in the pit, the cytoplasm of the cover 
cells and the underlying ground substance of the connective tissue 
are stained brown, the connective tissue usually being of a lighter 
shade than that of the cover cells and mucus. In some cases 
the mucus is continuous with a similarly colored mass occupying 
the place of a cover cell and extending down to the basement 
membrane, looking as if the cover cell had become converted into 
one;i7ass of mucus. The mucus is never seen in such intimate 
connection with a flagellated cell. In some of my formalin-gold 
chloride preparations the surface of the cover cell is studded with 
very distinct long processes, three to five times as large as those 
noted above. They look like stout cylindrical cilia with rounded 
free ends to which are usually adhering small bits of mucus. 
In all of these formalin- gold chloride preparations the cell sub- 
stance is very badly shrunken and in every respect the sections 
suggest very poor preservation. In fact whenever the sections 
