C(ELENTERATA. 



247 



a central cavity with one 



opening. The animal 



may be compared to a 



bag with a two-layered 



wall,andtentacles around 



the opening. It buds, 



and also reproduces by 



eggs. The buds, when 



adult, become detached 



from the parent. 



In most of the other 



Hydroids the colony is 



permanent, and support- 

 ed by a horny skeleton. 



There are two kinds of \ 



Polyps in each colony, FlG ^_ Hydra: 7; ith teutacle8 fallye *^d- 



one for feeding and the ed ; 3, creeping; 5, budding. 



other for reproduction. Sometimes the reproductive 



Polyps are separated 

 from the stock in the 

 form of little Jelly- 

 fishes. The larger 

 Jelly - fishes belong 

 to another group 

 the Acalephce 

 and are produced as 

 told on page 212. 



The Jelly-fish has 

 a soft, gelatinous, 

 semi-transparent,bell- 

 shaped body, with 

 tubes radiating from 

 the central cavity to 

 the circumference, 



FIG. 192. Hydroid (Serfutoria) growing on a Shell, and with the margin 



