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CLASS IV. 
POLYPI(1). 
Our fourth class of the Radiata or Zoophytes has been thus 
named because the tentacula which surround their mouth give 
them a slight resemblance to an Octopus called Polypus by 
the ancients. The number and form of these tentacula vary. 
The body is always cylindrical or conical, frequently without 
any other viscus than its cavity, and frequently also with a 
visible stomach to which adhere intestines or rather vessels 
excavated in the substance of the body like those of the Me- 
dusz ; in this latter case we usually find ovaries also. Most 
of these animals are capable of forming compound beings, by 
shooting out new individuals, like buds. They also, how- 
ever, propagate by ova. 
(1) This class of animals, although nearly at the end of the series, is one of the 
largest, and certainly the most singular of the whole. Suchis the enormous accu- 
mulation of the stony envelopes formed by them in certain seas, that islands are 
produced, coasts extended, and harbours blocked up by them. The late lamented 
"M. de Lamarck has even hazarded the idea, that the calcareous strata of the globe 
may have been produced by them. Polypi were formerly considered as stony 
plants. Imperati( 1699) was the first who doubted their vegetable nature, and Trem- 
bley’s observations on the Hydra (1740) put the question at rest. Since that 
period, our knowledge of them has been considerably increased by the labours of 
Ellis, Boccone, Cavolini, Lamouroux, &c, &c. Am. Ed. 
