140 
, MARINE INVERTEBRATES 
Genus Cassiopeia 
Pelagia cyanella, 
C. frondosa. This species 
has a circular disk, on the 
margin of which are sixteen 
sense-organs (tentaculocysts), 
but no tentacles. The lower 
end of the manubrium, which 
in other jellyfishes is an open 
mouth, is closed by eight arms 
which emanate from it and are 
usually extended laterally, ly- 
ing parallel to the disk. These 
arms are much branched, and 
the branches, in turn, have 
numerous appendages. Some 
of these appendages look like 
little polyps and have mouths 
surrounded by crowns of ten- 
tacles ; others are ovoid bodies 
without external openings, but 
with a central cavity connected 
with vessels leading to the 
arms. The former are mouths, 
but the function of the ovoid 
bodiesisnot known. Although 
able to swim freely, Cassiopeia 
lies usually on its back, as if 
attached, and languidly opens 
and closes its disk, rarely 
changing its position. Its arms, 
extending upward, appear like 
the fronds of alge. These 
jellyfishes are common on the 
Florida coast, huddled together 
on the sands of the coral reefs. 
(Plate XLIV.) 
