240 COMPARATIVE ZOOLOGY. 
ping their sides, like the opening and shutting of an um- 
brella, with great regularity. They are frequently phos- 
phorescent when disturbed. Some 
are quite small, resembling little 
glass bells; the common Avwrelia is 
over a foot in diameter when full 
grown; while the Cyanea, the giant 
among Jelly-fishes, sometimes meas- 
ures five feet, with tentacles forty 
feet long. When dried, nothing is 
left but a film of membrane weigh- 
ing only a few grains. 
There are two representative types : 
Fre. 191A Meausa, seenin the Lucernarta, the Umbrella-acaleph, 
Profile and from below, having a short pedicel on the back 
showing central polypite, = 2 f 
radiating and marginal for attachment; tentacles disposed in 
canals. fol 2 if ant pe h 
elght groups around the margin, the 
eight points alternating with the four partitions of the 
body-cavity and the four corners of the mouth; not less 
than eight radiating ca- 
nals, and no membra- 
nous veil. The common 
species on the Atlantic - 
shore, generally found 
attached to eel-grass, is 
an inch in diameter, of Fra. 192. —Zacernaria awricula attached to a 
A piece of sea-weed; natural size. The one 
a green color. Dzsco- 
on the right is abnormal, having a ninth 
phora, the ordinary Jel- "of tentacles, 
ly-fish, is free and oceanic. It differs from the Lucernaria 
in its usually larger size and solid disk, four radiating ca- 
nals, which ramify and open into a circular vessel, and a 
“veil,” or shelf, always running around the mouth of the 
disk." 
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