748 THE AMERICAN NATURALIST. | [Vor. XXXIV. 
nettling filaments, acontia, may escape. The cinclides are 
sometimes borne on tubercles, which are then called cinclidial 
tubercles. In rare cases, as, for instance, Epiactis (Fig. 8), the 
eggs seem to be carried in pits on the column, and the young 
may be retained in these egg pits for a considerable period. 
The oral edge of the column is at times characterized by a 
series of enlargements that are probably neither tubercles nor 
tentacles, but have been called marginal spherules. Usually 
the oral edge of the column passes directly over into the tenta- 
cle-bearing portion of the oral disk. In some species, however, 
a fold is interpolated in this region, giving rise to what has been 
called a collar. The column, though usually strictly naked, 
may be covered with a slight secretion, cuticula, which may be 
firm and rough, as in Phellia, or slightly adhesive, so as to 
accumulate sand particles, as in Epizoanthus. 
The oral disk carries the circle of tentacles. These are hol- 
low processes from the wall of the disk and are usually pointed, 
though sometimes blunt or even club-shaped, as in Eloactis 
(Fig. 4). They are usually firmly attached to the oral disk, but 
in Bolocera (Fig. 6) the region of attachment is marked by a 
well-developed circular muscle, by whose contraction the base 
of the tentacle may be much constricted or even cut through, 
thus setting the tentacle free. As a rule, the tentacles cover 
a single circular area intermediate in position between the 
mouth and the margin of the oral disk. In Cerianthus (Fig. 
21), however, they form two distinct bands, one marginal (prin- 
cipal) and the other circumoral (accessory) The mouth lies 
in the center of the oral disk and is generally surrounded by 
swollen lips. In Bicidium a portion of the lip is so much 
enlarged as to produce a projecting proboscis, the conchula. 
Of the internal structure of the sea anemones little need be 
said in this connection, as the features upon which the follow- 
ing key is based are chiefly external. The mouth leads into a 
gullet or esophagus, which opens at its pedal end into the one 
internal cavity possessed by the animal, the gastrovascular space. 
This is partly divided by membranous partitions, or mesentertes, 
that start from the inner surface of the column wall and pro- 
ject centrally. From the inner edge of the mesenteries come 
