ACTINOIDA. 683 



perpetually in motion, producing a continuous current of water. 

 They are not under the animal's control from the period of its 

 escape from the egg. Even in the egg, and when the animal is 

 at rest, these cilia are in motion, their action wafting small por- 

 tions of organic matter to the mouth of the animal, itself incapa- 

 ble of going after other food, and thus supplying its wants. By 

 means of their tentacles, however, Polyps are able to seize upon 

 larger prey. 



FIRST ORDER. ACTINOIDA, (ACTINOIDS,) (Gr. dxxJj/, aktin, a ray, 

 Ray-like,) SEA- ANEMONES and CORALS. 



The name given to these animals refers to the radiated dispo- 

 sition of the tentacles, which, when expanded, sometimes resem- 

 ble the petals of a flower ; when contracted, the mass assumes 

 a lemon-like shape. The order includes, however, not these 

 actiniae or flower-shaped genera alone, which do not secrete a 

 coral, but others also, which are coralligenous. 



The exterior surface of the Actinoids is either fleshy or leath- 

 ery, slimy, and exceedingly sensitive. The mouth is simple 

 and bordered with tentacles, it is situated above, while in the 

 Star-fish, it is beneath. Each of the tentacles is a tube, the walls 

 of which are formed of longitudinal muscular fibres. By the 

 contraction of these fibres, the animal can shorten the tentacles 

 in all directions. Around the entire tube are circular fibres. 

 These pull the tentacles in succession, so as to elongate it to three 

 or four times its usual length, thus enabling the animal to seize 

 its larger prey. The interior cavity or stomach, is a simple sac, 

 which the animal contracts or shuts at pleasure. The digestive 

 power is great and rapid, commencing to act as soon as the food 

 is within the cavity. Fish, Crabs, and Shell-fish, are speedily 

 assimilated, the harder parts being ejected in the course often or 

 twelve hours; and the juices produced by the influence of the 

 walls of the stomach, are diffused in the lower cavity, into which 

 the water which came in with the food is also poured. The 

 Actinoids have " no blood, no vessels, no respiration proper, 

 though the contact of water produces a sort of respiration." 



he reproduction is both by division and by eggs. At first, 

 the young have but five or ten tentacles, but these steadily in- 

 crease until they become almost innumerable, though uniformly 

 " multiples of five." Lost parts, especially the tentacles, are 

 soon replaced. If the body be cut into several parts, each may 

 survive and become a complete animal. Actiniae can endure 



