SERTULARIADJE. 1 25 



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 

 j)olyp, 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 aipressina 

 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 

 ScrtulariadcE 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 pinnse 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 



