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TEXTBOOK OF ZOOLOGY 



Order Trachylina. — This order includes two suborders of hydro- 

 medusae which come from the egg- directly with no polyp stage. 

 Campanella and Liriope are generic examples. 



Order Hydrocorallina. — This group resembles the corals by produc- 

 ing strong calcareous skeletons. They have extensive, branched hy- 

 drorhiza and powerful nemato cysts (stinging 'bodies). Rudimentary 

 medusalike bodies develop on the coenosarcal canals. Millepora, the 

 staghorn or stinging coral, as it is called, is a good example. 



Fig. 61. — Physalia, the Portuguese man-of-war a floating colonial coelenterate. 

 (From Hegner, College Zoology, published by The Macmillan Company.) 



Order Siphonophora. — This is a pelagic order of colonial coelen- 

 terates with extreme polymorphism. A common tube of the coenosarc 

 unites the five kinds of individuals of the colony, and this cavity is 

 continuous from one individual to another. The blind end of the 

 coenosarcal tube is an air-filled, bladderlike float (pneumatopJiore) 



