SECT. iv. ALCYON ZOOPHYTES. 1 2 1 



folds forming so many longitudinal chambers open at 

 their lower extremity. The whole of the surface of the 

 interior, the walls, the stomach, and the septa or divi- 

 sions, are covered with fine cilia, by whose vibrations 

 constant currents are maintained in the water which 

 bathes every part of the cavity freely entering at the 

 mouth. The polypes are carnivorous, living upon infu- 

 soria and minute particles of animal matter floating on 

 the water, which they seize with their mouth, or arrest 

 with their flexible and contractile tentacles. The food 

 is digested by the solvent juices in the stomach, and the 

 refuse is ejected at the mouth. 



The eggs of these polypes are formed and fertilized 

 among the vertical folds adjacent to the stomach. When 

 hatched, the larvae pass through the stomach and come 

 out at the mouth as active ciliated creatures, so like eggs 

 that the Alcyon zoophytes were believed to be oviparous. 

 However, in some of the genera they are discharged 

 through pores between the bases of the tentacles. 



The Alcyon polypes have multitudes of needle-like 

 spicules, rough with projecting knots. They are col- 

 lected into triangular groups at the foot of each ten- 

 tacle ; the cen- 

 tral and largest 

 point runs up 

 into the tentacle. 

 Towards the 

 lower end of the 

 polype, spicules 

 again occur scat- 

 tered through 

 the skin and 



Crowded into Kg 12g Spicula of Alcyonium digitatum. 



groups, as in fig. 



125. These, however, form short thick cylinders, each 

 end being dilated into a star of five or six short branches. 

 The spicules always contain an organic base hardened by 



