156 THE SEA SHORE 



with oyster shells that it is by no means an uncommon object in 

 the fishmonger's shop, from which we have often obtained live 

 specimens for the aquarium. 



When placed in sea water it gradually imbibes the fluid 

 surrounding it, becoming much swollen. Then little star-like 

 openings appear, the circumference of each of which protrudes so 

 as to form a little projecting tube. Finally, a crown of eight little 

 tentacles is protruded, and the mass, so uninteresting at first 

 sight, reveals itself as a colony of pretty polyps. 



In general structure the Alcyonium resembles the sea anemone, 

 but the firm body-wall of the colony is supported and protected to 

 some extent by the presence of minute spicules of carbonate of 

 lime; and it is interesting to note that while the tentacles of 

 anemones and corals make up a number that is a multiple of either 

 five or six, those of the Alcyonaria and the allied ' Sea pens ' are 

 always in multiples of four. 



