368 A. M. REESE 
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Fig. 18 A section of sensory epithelium of a canal of type 2; corresponding to 
that shown in the preceding figure. 
epithelium is the same as has just been described. In this region 
the columnar epithelium retains about the same character around 
the entire peripher}^ of the canal, being scarcely any thicker along 
the floor than in the m.ore distal regions. This is shown, diagram- 
matically, in fig. 14, e. 
In the part of the canal (of iy^e 2) between the wide spaces there 
is some differentiation in the columnar epithelium. This differ- 
entiation is greatest in the middle regions and disappears gradually 
as the wide spaces are approached. In this middle region, be- 
tween the wide spaces, the epithelium gradually becomes thicker 
as it passes from the slit to the floor of the canal, until, along the 
median line of the floor, it is about twice as thick as at the opening. 
This greater thickness is due to the greater length of the columnar 
cells. 
Along the median line of the floor of the canal is seen the same 
wide, shallow groove that was noticed in connection with canals 
of type 1 (figs. 14a, 18). The cells that form the bottom of this 
groove are quite distinct from the rest of the epithehal lining of 
the canal, and would seem to represent the sensory epithelium, 
though they possess no bristle-hke ends, and no nerve connections 
could be made out. They are simply long, tapering, columnar 
cells, each with a darkly stained nucleus near the basal end. They 
stain less strongly than the cells on either side, so that they are 
always distinctly differentiated from them, as is shown in fig. 
18, sc. The surrounding cells are, perhaps, narrower than those 
just described, and become shorter as they pass outward and 
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