CCELENTERATA. 



247 



a central cavity with one 

 opening. The animal 

 may be compared to a 

 bag with a two-layered 

 wall, and tentacles 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, 

 one for feeding and the 

 other for reproduction. 



. I'Jl.- Hydra: 2, with tentacles fully extend- 

 ed ; 3, creeping ; 5, budding. 



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 Acalepha 

 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, 



Fi.192.-Hydroid(SerMaria) growing on a Shell, 



and with the margin 



