122 THE STORY OF ANIMAL LIFE 



marine forms. They '* have a free-swimming 

 larva, which becomes fixed after a time, and 

 gives rise to the adult Colonial forms. The 

 zooids of the latter have each an independent 

 head with a crown of tentacles, called the Lopho- 

 phore (Crest-carrier) ; but the fixed ends of their 

 bodies communicate with one another. The hard 

 covering of the colony, which retains its form 

 after the animal is dead, is a kind of hardened 

 skin : the apparent " cells " are the openings 

 through which the individual zooids protrude 

 themselves. Sometimes certain of the zooids 

 undergo modification for special purposes: in 

 this way are formed the " avicularia," snapping 

 appendages, probably defensive in purpose, so 

 called because they open and shut like a bird's 

 beak. There are two divisions of the Polyzoa, 

 the Ectoprocta and the Endoprocta. Among the 

 latter there is found a form which is not colonial. 

 Phoronis, a curious worm-like animal, which 

 has a larval form called Actinotrocha is sometimes 

 placed in classification near the Polyzoa, which/ 

 it resembles in possessing a crown of tentacles 

 (Lophophore). 



CHAPTER XII 



THE ECHINODERMATA 



EVERYBODY knows the Star-fish and many peo- 

 ple know the Sea-Urchin. An " urchin " is not a 

 name for a naughty little boy, but the French 

 (our sin) for a hedgehog. A Sea-Urchin is there- 

 tore a "Sea-Hedgehog," a name very appropriate 



