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ChHPAUP XeV EL. 
CCELENTERATA. 
POLYPS AND JELLY-FISHES. 
Thread-cells or Urticating Organs.—Sertularie.—Campanulariade.—Hydrozoie 
Acalephx.— Meduside.— Lucernariade.— Calycophoride.— The Velella.— The 
Portuguese Man-of-war.—Anecdote of a Prussian Sailor—Alternating Fixed 
and Free-swimming Generations of Hydrozoa.—Actinozoa.—Ctenophora—Their 
Beautiful Construction.—Sea-anemones.—Dead Man’s Toes.—Sea-pens.—Sea- 
rods——Red Coral.—Coral Fishery.—Isis hippuris.—Tropical Lithophytes.— 
History of the Coral Islands—Darwin’s Theory of their Formation— The 
progress of their Growth above the level of the Sea. 
Despite the low rank they occupy in the hierarchy of animal 
life, the Coelenterata, comprising the numerous families of the 
Jelly-fishes and Polyps, play a most important part in the house- 
hold of the ccean, for the sea is frequently covered for miles 
and miles with their incalculable hosts, and whole archipelagos 
and continents are fringed with the calcareous structures they 
raise from the bottom of the deep. 
Their organisation is more simple than that of the preceding 
classes, for they have neither the complex intestinal tube of the 
polyzoa or the sea-urchins nor the jointed rays or arms of the 
star-fishes ; their whole digestive apparatus is but a simple sac, 
and their instincts are reduced to the mere prehension of the 
food that the currents bring within reach of their tentacles, or 
to the retraction of these organs when exposed to a hostile 
attack. 
But, simple as they are, they have been provided by Nature 
with a comparatively formidable weapon in those remarkable 
“ thread-cells,” or urticating organs, which are so constantly met 
with in their integuments, and chiefly in their tentacles. 
The thread-cells are composed of a double-walled sac having 
its open extremity produced into a short sheath terminating in 
