Sle ON THE GENUS LUCERNARIA. 
diata and campanulata, have capitate extremities, and in 
this part the central cavity is enlarged, and the outer mem- 
brane manifestly thickened. In L. octoradiata these heads 
are quite round, and have a diameter 0°15 mm. on tentacles 
which are about 15 mm. long. In L. campanulata, on the 
contrary, they are discoid, and often have an acetabular depres- 
sion in the centre; their diameter reaches 0°4 mm. in tenta- 
cles of 1-6 mm. length, so that they are here proportionally 
of a much more considerable size than in those of the former 
species. 
In L. campanulata the fine tentacles situated on the under 
side of an arm (figs. 4, 5) are of peculiar construction. They 
are, for instance, very short, and the base expands into 
a round, boss-like projection (6), 0°4 mm. in length, which is 
a thickening of the outer membrane, and is filled with thread- 
cells as fully as the button-like end itself. These five bosses 
are very regularly arranged ; the lowest and central one is the 
largest, whilst the two on either side regularly diminish im size. 
Milne-Edwards did not recognise their place on the base of 
the small tentacles, and describes them as vesicles, and 
probably as representing organs of secretion. 
The outer membrane of the button of the tentacle and of 
these boss-like thickenings contains a layer of dense, pali- 
sade-like, scimitar-shaped thread-cells, which in L. campa- 
nulata are 0'015 mm. long and 0-005 mm. wide, and between 
these some larger oval ones are irregularly distributed, having 
in the same species a length of 0°017 mm. and a width of 
0:007 mm. These knobs contain, besides the thread-cells, 
granules of yellow pigmeut, which give them a yellow colour, 
often very bright. 
The animal can exert preheusile movements with its 
tentacles, and L. campanulata, by means of its disc-like knobs, 
can attach itself as with suctorial acetabula. 
5. Marginal papille.—In some species peculiar papille 
occur, regularly placed on the margin of the bell between 
the arms. These were first mentioned by O. Fabricius in 
his L. auricula, and I have examined them myself in ZL. 
octoradiata, i which species they have been described by 
all earlier observers. 
These papille (fig. 1 and 3, ~) consist of protrusions of the 
two membranes with the intermediate gelatinous substance, 
and in essential structure resemble the tentacles. They are 
not placed precisely on the margin of the bell, but rather 
under it, so that they appear like protrusions of the gela- 
tinous disc. They have a large internal cavity, which com- 
