270 ON THE GENUS LUCERNARIA. 
cavity —the radial canals—and their orifice (#) is surrounded, 
on the exterior, by a thickened border, and has scarcely any 
visible canal. 
The thread-cells are formed in the parietal cells of these 
follicles, and falling then into the cavity, which they quite fill, 
they can be squeezed out of the mouth. These follicles have 
thus, in all respects, the typical structure of a gland, and on 
that account claim a special interest. 
The thread-cells in these receptacles, like those in the yellow 
spots on the outside of the Lucernaria, where similar recepta- 
cles are of but very rare occurrence, are of an oval form, and 
0-011 mm. long; when shot out, the apparently spiral thread is 
seen to be placed upon a hollow pedunele, 0:01 mm. long, and 
furnished on the exterior with reflexed setze. The capsule is 
then only 0-008 mm. long, and almost globular (fig. 15). 
3. Stem.—The bell narrows suddenly into the cylindrical 
stem, the end of which is closed and expanded in a disc-like 
manner to form the usual adhesive organ of the animal, 
and which serves the same purpose as the foot of the Actinia. 
The stem is a direct continuation of the gelatinous dise, 
for as the natatory sac is divided into four points at the bot- 
tom of the cup, and is also at these points attached to the 
disc, the stem contains no continuation of that organ, and 
its wall, like that of the disc, consists of the outer and 
inner formative membrane and the intermediate gelatinous 
substance. 
In a transverse section of the stem, which can easily be 
made in L. campanulata, in which it contains no muscles, 
and is scarcely at all contractile (figs. 10, 11), the wall is 
seen to project on the interior into four longitudinal ridges, 
which are so placed as to meet above the angles of the 
natatory sac, as has been described by most writers. On the 
under side of the foot they present the appearance of four 
spots, and in the lower part of the stem of L. octuradiata—in 
which, however, on acccount of its great contractility, I have 
never been able to obtain a satisfactory view—they appear 
to be so much developed as to meet and join in the axis, so 
as to subdivide the simple cavity into four tubes, separated 
from one another, but communicating above (fig. 13, ). 
In the centre of the under side of the foot there is a de- 
pression, which appears to have been first described by 
Lamarck as a cecal pit (figs. 11, 12, &), projecting into 
the gelatinous substance. In L. campanulaia, where the 
stem is non-contractile, these relations can be easily studied. 
In a foot-dise 0°44 mm. in diameter this pit was 0°074 mm. 
