214 
THE OCEAN WORLD. 
the east, west, or north ; others, on the contrary, grow only on these 
exposures, and never on the south, altering their position, however, 
according to the latitude, and its relation to the Equator. 
The Sertulanadm have a horny stem, sometimes simple, sometimes 
so branching that they might readily enough he mistaken for small 
plants, their branches being flexible, semi-transparent, and yellow r . 
Their name is derived from Sertum, a bouquet. Each Sertularia has 
seven, eight, twelve, or twenty small panicles, each containing as 
many as five hundred animalcules ; thus forming, sometimes, an asso- 
ciation ot ten thousand polypes. “ Each plume,” says Mr. Lister, in 
reference to a specimen of Plumularia cristata, “ might comprise from 
four to live hundred polypi ;” “ 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 giving six thousand as 
the tenantry of a single polypidom, and this on a small species.” On 
Sertularia argentea, it is asserted, polypiers are found on which there 
exist not less than eighty to a hundred thousand. 
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 
polype, are grouped alternately. The head of the animal is conical, 
the mouth being at the top surrounded by twenty to twenty-four 
tentacles. These curious beings have no digestive ca vity belonging to 
themselves; the stomach is common to the whole colony — a most 
singular combination, a single stomach to a whole group of animals ! 
Never have the principles of association been pushed to this length 
by the warmest advocates of communism. 
Certain species belonging to the 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 cells; 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 lightly sometimes to 
the right, sometimes to the left. The vibratile cells fading afterwards, 
