98 REDFERN, ON FLUSTRELLA HISPIDA. 
great care, by the aid of the camera lucida; in the single 
instance there were twenty-seven. Each tentacle is hollow, 
covered by a thick layer of ciliated epithelium, easily de- 
tached. It is quite remarkable how rapidly these epithelial 
cells become distended and destroyed when fresh water is 
added; and as this is the case also with the cells of other 
parts of the animal, it is not surprising that fresh water 
instantly destroys it. Fig. 5 represents a portion of a 
tentacle with its epithelium in the natural state; fig. 6 
the tentacle divested of its epithelial covering ; and fig. 7 
shows the action of fresh water upon the epithelial cells. 
The pharynx and cesophagus are lined throughout by 
ciliated and columnar epithelium. The stomach is separated 
from the oesophagus by a distinct and complete valve which 
never allows the alimentary matters to regurgitate. The 
cesophageal portion of the organ is cylindriform, the body is 
greatly dilated having a pouch-like dilatation on its great 
curvature, and being gradually narrowed towards the pyloric 
aperture, where the stomach can be shut off from the intes- 
tine, apparently by a contraction of its muscular wall (py- 
loric valve). Over the whole of the stomach, the epithelial 
cells contain a nucleus and deep-red, granular contents. 
Those of the cul-de-sac, and in the great curvature, and those 
at the pyloric end, are ciliated; but no cilia are observable 
in the other parts, nor in any portion of the intestine. The 
action of the cilia of the stomach is remarkably beautiful 
when viewed under the microscope, and produces a rapid 
rotatory motion of the contents of the cul-de-sac, or of the 
pyloric end, in the axis of these parts respectively. 
To the stomach succeeds a dilated portion of the intestine, 
where the alimentary matters are retained for some time, and 
converted into elongated consistent pellets. The wall of this 
portion of the canal has an epithelium, the cells of which 
contain deep-red granules like those in the stomach-cells, 
but much fewer in number. Beyond this the intestine is 
considerably contracted, and its wall becomes so thin that it 
is often torn during the dissection, in tearing away the tu- 
bular sheath of the tentacles, formed of the soft, protrusible 
portion of the cell. Through this membrane the anus opens 
externally. I have never noticed the discharge of alimentary 
matters, except at the moment of protrusion of the tentacles, 
when the pellet to be discharged escapes from within the 
crown of tentacles, and commonly falls through between two 
of them to the exterior. 
Muscular system.—The retractor muscular fibres are best 
seen, im situ, in preparations which have been preserved in 
