THE POL VPIERS. 89 
be mistaken for small plants, their twigs being flexible, semi-trans- 
parent, and yellow. Their name is derived from the Latin sertum, 
a bouquet. Each Sertularia has seven, eight, twelve, or twenty 
small panicles, each containing as many as 500 animalcules, 
thus sometimes forming an association of 10,000 polypes. The 
Sertularia falcata reminds one, from the elegance and delicacy of 
its branches, of the beautiful Mimosa. This polypier is now classed 
with the Bryozoas. 
The little cells in which the polypes lodge are not always 
arranged in the same manner. Sometimes they are on one side of 
ZOANTHA THALASSANTHOS, 
the stem only, sometimes on both; now they stand like the pipes 
of an organ, now they wind in spirals, or arrange themselves in 
rings about a common axis. 
The Actiniform polypes are divided into two tribes according 
to the number of their tentacles. In the one the number is six, 
ora multiple of six; these are the Zoantharia. In the other, the 
A lcyonide, the characteristic number is eight. 
The Zoantharia comprehend three distinct classes: the Ant- 
pathide, the Madreporide, and the Actinide, which constitute the 
zoanths proper. These Zoantharia are elegant zoophytes, which 
occupy an intermediate rank between the polypiers and the sea 
anemones, of which we shall speak in a future chapter. They 
are often joined together in considerable numbers to the same base; 
