JELLYFISH, the medusa-stage of Hydro zoa (q.v.), but more especially the common name of Scyphozoa (formerly Discomedusa), the second class of the phylum Calenterata (q.v.). A familiar example is the common large jellyfish of the coast of New England, Aurelia flavidula. It sometimes reaches the diameter of 10 inches; its umbrella-shaped body is convex and smooth above, and from the under sides hang down four thick oral lobes which unite to form a square mouth-opening also giving off four tentacles. The margin of the umbrella or disc is fringed and bears eight eyes which are covered by a lobe. Just under the surface are seen the water-vascular canals, branching out from four primary canals radiating from the stomach. When in motion, the disc contracts and expands rhythmically, on the average from 12 to 15 times a minute.
Tice Aurelia spawns late in the summer, the females having yellowish ovaries, while the sperm glands of the males are roseate in hue. The eggs are fertilized in the sea and the cili ated pear-shaped larva by October sinks to the bottom, attaching itself to rocks or shells, finally assuming a hydra-like shape, with often as many as 24 long slender tentacles. This is the Scyphistoma stage in which it remains about 18 months. From this it passes into the Strobila stage in which the body divides into a series of cup-shaped discs, each of which is scalloped on the upturned edge. These discs separate one after the other in March and swim away as miniature jellyfishes called Ephyra. The
Ephyra is at first about a fifth of an inch in di ameter, and becomes a fully formed Aurelia in April, reaching maturity in August. Another but less common jellyfish on the coast of New England and in the north Atlantic is the great Cyanea arctica, or "blue jelly,'" which is nearly • two feet in diameter, sometunes from three to five, and with very long string-like tentacles, sometimes extending from 20 to 100 feet, which are filled with stinging or lasso-cells (tricho cysts), so that the animal is poisonous to fisher men and bathers. While these forms undergo a metamorphosis, in fact, an alternation of gen eration, other kinds, as Pelagia, etc., are known to develop directly from the egg, and even the aurelia under exceptional circumstances does not pass through the scyphistoma stage. The jellyfishes are divided into a number of groups. They are most numerous in the tropical seas, comprising forms of great beauty. Consult Agassiz and Mayer,
from the Fiji Islands> (in Bulletin of the Museum of Com parative Zoology, Vol. XXXII, Cambridge 1899) ; Romanes, C. J.,