THE TUBIPORA. 115 



spicula like those of some sponges, interspersed 

 through it and containing numerous canals, is studded 

 with polyps like hydras. These are all seated in 

 little cells on the surface, from which they can pro- 

 trude and expand their arms. 



The different species assume a variety of forms ; 

 all of which, however, are fixed on other substances, 

 as stones and shells. The upper 

 surface is dotted with cells, in 

 which the polyps reside ; and when 

 they are all protruded, they cover 

 the common pulpy mass with 

 clusters of flowers, or stars. From 

 the cavity of the stomach of each 

 polyp of Cydonium of which a 



single one is here represented, POLYP OF THE 

 , , , . CYDONIUM. 



removed from the mass and magni- 

 fied a tube is extended, conveying nutriment to the 

 general mass ; a tubular filament also opens into the 

 stomach, which contains the germs of a future pro- 

 geny. When mature, they pass from the tube into 

 the digestive cavity of the parent polyp, and thence 

 through the mouth into the sea. 



Though these polyps and the general mass par- 

 ticipate in one common life, as far as nutrition is 

 concerned, yet there appears to be no community of 

 feeling between them, for they expand and contract 

 independently of each other. When one is rudely 

 touched, it withdraws itself; but the rest remain 

 unaffected. Local injury on one portion of the 



