SPONGES, ZOOPHYTES, AND SEA-FIRS. 



41 



will recover his equilibrium, and once more appear on his 

 doorstep. About the same time the dingy crust on the shell 

 will change its appearance, and show you a delicate waving 

 forest of little pink creatures, which spread out in the water 



Fia. 12. -Diagram reprcs. nting the individual persons or - 

 zooids in a colony of Hydractinia echinata. a, nutritive 

 person with tentacles extended ; b, sensitive person with 

 ab< rted tentacles ; c, reproductive persons bearing clusters 

 of sporosacs. At the bases of the persons are shown the 

 stout protective spines. After Allman. 



like miniature flowers. The whole crust constitutes a zoophyte 

 colony, the tiny flowers are the members of the colony, and 

 are called polypes, or better, zooids. We have begun our 

 study of the sea-nettles with a colony of this kind, rather 

 than with the more familiar sea-anemones, because the 



