212 THE OCEAN WORLD. 



exposures, and never on the south, altering their position, however, 

 according to the latitude, and its relation to the Equator. 



The Sertulariadse 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. 

 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 of ten thousand polyps. " Each plume," says Mr. Lister, in 

 reference to a specimen of Plumularia cristata, " might comprise from 

 four to five hundred 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 giving six thousand 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 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 

 polyp, 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 cavity 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, 

 the embryo attaches itself to some solid body, a tubercle is formed, 



