510 PENNATULA. ASTEROID POLYPES. 



When it is irritated or alarmed, a vivid emission takes place ; but 

 this soon dies away. When frequently struck by the waves, it 

 is possible that they may continue the display with little inter- 

 ruption ; but observation proves that, when preserved in calm 

 water, they do not voluntarily disengage light, although they 

 readily show it if disturbed. The accompanying figure repre- 



FIG. 718. VERKTILLUM. 



sents a genus of Alcyonian Polypes nearly allied to the Penna- 1 

 tula. The Virgularice and Pavonarue, which also belong to this t 

 group, are of an exceedingly elongated and slender form, some of; 

 them measuring three or four feet in length. They are com- 1 

 monly known as " Sea-rushes." 



1157. The next group of Asteroid Polypes includes manyj 

 well-known species, such as the Red Coral, the Gorgonit orj 

 Sea-fan, the Antipathes or Black Coral. In all of them thej 

 structure of the Polypes is nearly the same ; and the differences 

 of the polypidom chiefly relate to the portion, in which the 

 solidification of the structure has taken place to the greatest 

 extent. It will be recollected that, in the true Alcyonia, the 

 calcareous or silicious spicula are deposited, as in the Sponges, 

 through the whole mass ; and that with the exception of the 

 fibrous bands which interlace between the canals, no one portion 

 is harder than another. Now in the group at present under 

 consideration, a solidification takes place in the centre or axis 

 of the polypidom, and often in the integument also. Almost all 

 the species included in it have an arborescent form ; and so much 

 does the flexible axis of many kinds resemble the stem of a plant, 

 that, even so late as the year 1825, the celebrated Blumenbach 



