CORALLINE. 



229 



The arms of the polyps are at times subject to violent agitation : 

 the tentacula become much excited. If this excitement continues, 

 the tentacula can be seen to fold and roll themselves up, as shown 

 in Fig. 86. If we look at the expanded disc, we see that the eight 

 tentacula are attached to the body, around a space nearly circular, 

 in the middle of which rises a small protuberance, the summit of 

 which is occupied by a small slit forming two rounded lips. rm "'~ : ~ 



This is 



Fig. 85. 

 Coral Polyp (Lacaze-Duthiers). 



Fig. 86. 

 Another form of Coral Polyp (Lacaze-Duthiers). 



the mouth of the polyp, the form each assumes is very variable, but 

 it is well represented in Fig. 86, where the mouth is well seen. 



A cylindrical tube connected with the mouth represents the 

 oesophagus or gullet ; but all other portions of the digestive canal 

 are very rudimentary. The oesophagus connects the general cavity 

 of the body with the exterior world, and looks as if it were suspended 

 in the middle of the body by certain folds, which issue with perfect 

 symmetry from eight points of its circumference. The folds which 

 thus fix the oesophagus form a series of cells, above each of which it 

 attaches itself, and supports an arm or tentaculum. 



