96 THE AMERICAN MIDLAND NATURALIST 
as to completely mask the primary tubular character of the 
gill filaments. These outgrowths at the bases of the filaments 
which bind the filaments together into the lamella or plate, 
are broken at irregular intervals (o-fig. 1 and 2) giving rise 
at these interruptions to the ostia or water openings into the 
water tubes (w. t. fig. 1 and 2). 
Figure 3 shows a single lamella highly magnified. The 
sketch shows the lamella to be covered with ciliated columnar 
epithelium of which three kinds may be distinguished. These 
may be called from their positions on the filament, frontal (f), 
latero frontal (1.f.), and lateral (1). 
The cells of the frontal epithelium are ordinary columnar 
epithelium averaging 3 microns in length. They rest on a 
continuous base of connective tissue which extends along the 
lamella bending into each filament, and is only interrupted at 
the ostia. The cytoplasm of these cells is very granular espe- 
cially near the marginal end while the nucleus is at the base 
of the cell or better, the distal end. The nucleus in a few of 
the cells is found near the middle of the cell. Some of the 
cells are without doubt mucous gland cells and occasionally 
one may be seen of the characteristic goblet cell appearance 
which has discharged its secretion of mucous. From the ap- 
pearance of these epithelial cells it would appear that any of 
them can function either as an epitheleal ciliated cell or a 
glandular cell. The cilia borne on these cells vary in length 
- from one to two microns. The cells are on the average one 
micron or less in diameter giving a ratio of length to width 
ofS: A, 
Adjacent to the frontal epithelium on either side of the 
lamella is found the lateral-frontal epithelium. The distin- 
guishing character of this tissue is the remarkable length of 
the cilia and the comparative width of the cells. So long are 
these cilia that they bridge the space between the filaments 
and are entangled with those from the opposite cells of latero- 
frontal epithelium and for this reason the length of these cilia 
must be estimated rather than measured. Their estimated 
length is about four microns. These cells are very scant com- 
pared to the number of the others; usually only four or five 
cells occur on each side of the filament, one filament was found 
