4 



On Coral Reefs aiid Islands. 167 



they exceed them in the size of their flowers; for a breadth of 

 two and three inches is common. The polyps here alluded to, 

 along with the coral polyps allied, constitute the order or division 

 of zoophytes called Actinoidea.* 



The Actinias- are entirely fleshy, and usually live attached by 

 their lower extremity to the submerged rocks of the shores. 

 The mouth, at the centre of the flower-like disk forming the 

 summit of the animal^ is a simple opening without teeth or ap- 

 pendages of any kind. The tentacles — the petals of the flower 

 — aie tubular organs, and communicate internally with the inte- 

 rior cavity of the animal. The animal contracts, when disturbed, 

 and conceals the flower by rolling inward over it the margin 

 bearing the tentacles; and in this state it seems like a lifeless 

 lump of animal matter. Left quiet for a whilcj it again expands 

 and appears as before. This expansion is produced by receiving 

 water into the interior from without, mostly through the mouth, 

 and thus filling the tentacles and sweUing out its fleshy body. 

 They are generally found expanded with the mouth wide open to 

 receive their prey. As they are fixed to the rocks, they must 

 - wait for their food to come to them. When a crab, shell-fishj 

 or anything alive, within the capabilities of their bodies^ comes 

 within reach, they usually secure it by closing upon the victim 

 the tentacles, (which commonly have a stinging power,) and 

 pushing it into the mouth. In many species the tentacles are too 

 short to aid in capturing food except it be by stinging. These 

 organs subserve also the purpose of aerating the blood, a function 

 m which all parts of the body are more or less concerned. 



The interior of the actinia contains a cylindrical stomach sus- 

 pended from the disk, which opens at bottom into the general 

 cavity of the body. This general cavity, below the stomach 

 and around it, is divided into compartments by radiating fleshy 

 lamellse, the larger of which in their upper part connect the stom- 

 ach with the sides of the animal. The most important function 

 of these lamellae is that of reproduction, some being spermatic, 

 and the others bearing clusters of ova. These ova leave the 

 body by passing out through the stomach and mouth; but in 

 JJ^any instances this does not take place till the young animal 

 has proceeded from them. The refuse from the food after diges- 

 tion in the stomach is also ejected by the mouth, as this is the 

 only opening to the alimentary cavity. Other excrementitious 

 Matters, separated on the final elaboration of the chyle and its 

 ^siniilation, may escape through the sides of the animal, the 

 openmgs at the extremities of the tentacles, or in general by 

 ^y"^*^^'or pores or passages water may be ejected in the contrac- 

 tion of the animal 



This term 



