SERTULARIADA. 125 
seven, eight, twelve, or twenty small panicles, each containing as many 
as 500 polyps ; thus forming, sometimes, an association of 10,000 
polyps. “ Each plume,” says Mr. Lister, in reference to a specimen 
of Plumularia cristata, “might comprise from 400 to 500 polyps ;” 
“and a specimen of no unusual size now before me,” says Dr. 
Johnston, “with certainly not fewer cells on each than the larger 
number mentioned, thus gives 6,000 as the tenantry of a single 
polypidom, and this on a small species.” On Sertularia argentea 
it is asserted, polyps are found on which there exist not less than 
80,000 to 100,000. 
Each colony is composed of a right axis, on the whole length of 
which the curved branches are implanted, these being longest in the 
middle. Along each of these branches the cells, each containing a 
polyp, are grouped alternately. The head of the animal is conical, 
the mouth being at the top, surrounded by twenty to twenty-four 
tentacles. 
Certain polyps belonging to the same colony, which seem 
destined to perpetuate the race, have not the same regular form. 
Destitute of mouth and tentacles, they occupy special cells, which are 
larger than the others. The entire colony is composed exclusively of 
individuals, male or female. ‘‘ We have traced Sertularia cupressina 
through every stage of its development,” say Messrs. Paul Gervais 
and Van Beneden. “At the end of several days the embryos are 
covered with very short vibratile cilia ; their movement is excessively 
slow ; then, from the spheroid form which they take at first, they get 
elongated, and take a cylindrical form, all the body inclining slightly 
sometimes to the right, sometimes to the left. The vibratile cilia 
fading afterwards, the embryo attaches itself to some solid body, a 
tubercle is formed, and the base extends itself as a disc. At the 
same time that the first rudiments of the polyp appear, the disc-like 
tubercle throws out on its flanks a sort of bud, and a second polyp 
soon shows itself; its surface is hardened ; the polyp appears in its 
turn, and the same process of generation is repeated; a colony of 
Sertulariade is thus established at the summit of a discoid projection. 
At the end of fifteen days the colony, which has been forming under 
our eyes, consists of two polyps and a bud, which already indicates a 
third polyp. The sea-cypress, as this species is called, is robust, 
with longish branches decidedly fan-shaped, the pinnz being closer 
and nearly parallel to each other. The cells form two rows, nearly 
opposite, smooth and pellucid. The branches in some specimens 
are gracefully arched, bending as it were under the load of pregnant 
ovaries which they carry, arranged in close-set rows along the upper 
