CCELENTERATA. 



247 



a central cavity with one 

 opening. The animal 

 may be compared to a 

 bag with a two-layered 

 wall, and ten tacles aro u n d 

 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 . m _ Hydra: 2> with tem , cles fully extend , 

 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 {iSertularia) growing on a Shell, and with the margin 



