ON THE GENUS LUCERNARIA. 273 
municates by a wide opening with the vascular system 
and they have usually a round or oval form. Now and 
then they assume quite a tentacular form, and then have a 
projection (p’) at the end, which is filled with thread-cells, 
and they may be so elongated as to present exactly the as- 
pect of isolated tentacles. 
I have never found muscular fibres in the papille as in the 
tentacles; the muscular fibres of the margin of the bell (m” 
reach to them without entering into them, but the papille 
are in spite of this very contractile, and act like extremely 
strong acetabula. When the foot is loosened from its point 
of attachment, the Lucernaria can still hold itself fast by 
these acetabular papille, till it has again found a secure 
resting-place, and individuals are often met with adhering 
to Zostera-stems by both the foot and marginal papille, 
especially when in danger of being torn away by the force of 
the ebbing tide. 
The marginal papille are wanting in L. campanulata, but 
the knobs of the tentacles are in this case acetabular, and 
can be employed in a similar manner for the purposes of 
adhesion and fixation. 
6. Stomach.—At the bottom of the bell (fig. 4) the 
natatory sac (S), as has been already described, is divided 
into four triangular points (s), and which are attached by their 
extremities to the gelatinous disc. In this way four inter- 
spaces (e), which may be compared to bow windows, are 
formed in the natatory sac, and which lead from the cavity 
of the stomach into the radial canals. Above the situation 
where the natatory sac is subdivided into the four points is 
an annular thickening or elevation, which constitutes the 
prismatic oral tube (0), and which, as in Meduse, is probably 
a process of the natatory sac. A large quantity of gelatinous 
substance is developed between its two membranes, and its 
free margin is divided into four lobes, answering to its four 
sides, though these are often indistinct; and again, in most 
cases, subdivided into numerous minute lobules, and corru- 
gated. 
In the stomach we have consequently to consider, first, 
the true gastric cavity which lies between the four points of 
the swimming sac, and terminates below at the commence- 
ment of the stem, at the pot where the inner wall of that 
part is thickened into a circular ridge, by which its cavity 
appears, in most cases, to be separated from that of the 
stomach ; and secondly, the oral tube, which is very movable, 
and can be entirely folded upon itself. Lamouroux describes 
