Chapter XVII: Cœlenterata

POLYPS AND JELLY-FISHES.

Thread-cells or Urticating Organs.--Sertulariæ.--Campanulariadæ.--
Hydrozoic Acalephæ.--Medusidæ.--Lucernariadæ.--Calycophoridæ.--
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 345