172 THE OCEAN WORLD. 



They are habitually simple, and, if they present ramifications, these 

 are only exceptional. In nearly every instance, the tentacles exist to 

 the number of twelve, eighteen, tsventy-four, and even larger numbers, 

 and they form a sort of concentric crown to the animal. 



ZoantJms thalassantJws (Lesson), which has given its name to the 

 group, consists of large turf-like tufts of coral attached to a rock. 

 Its polyps are packed close together, and their expanded flower-like 

 heads have a curious resemblance to a mass of flowers in full bloom. 

 They are borne on bending root-like stems of pure white, interlacing 

 one with the other, surmounted by a fusiform or spindle-shaped body, 

 pediculate and swelling towards the middle, but truncate at the 

 summit, of a reddish-brown colour, marked with longitudinal stripes 

 more highly coloured ; its consistence is firm and parchment-like. 

 From the body issues a tube, narrow, muscular, contractile, and red 

 in colour, terminating at the summit in eight elongated arms or 

 tentacula, of a pure yellow, traversed by a nervure of the same colour. 

 The edges of these arms are fringed with fine pinnje, parallel to each 

 other, of a bright maroon colour, and resembling the barbs of a 

 feather. According to Lesson, the arms of this Zoauthus are kept 

 unceasingly in motion, thus producing in the water small oscillating 

 currents, in the course of which the animalcules on which the polyps 

 feed are precipitated into the stream leading to their mouths. 



The tendency to produce a calcareous or horny polypidom is a 

 property almost universal with animals of this class. Zoologists are 

 agreed in dividing them into three very distinct orders — namely, the 

 ANTiPATHiDyE, consisting of the genera Autipathcs, Cb-ripathes^ and 

 LeipatJm, in which the polypidom is of a horny consistence ; the 

 Madreporid^, in which the polypidom is calcareous and stony ; 

 finally, the Actinid.^, which produce no true polypidom. 



Antipathid^. 



We need not dwell upon this group, which is comparatively unin- 

 teresting. They somewhat correspond with the family of Gorg07iid(B 

 among the Alcyonaria, which they resemble m having the central axes 

 branching after the manner of a shrub; but the polyps have the 

 mouth surrounded with a crown of six simple tentacula. The axis 

 is of a harder and denser tissue than that of the Gorgonidse, and 

 presents on its surface small spiniform projections. The polypiferous 

 crust, with which they are covered, is in general very arenaceous, 

 and is so easily detached, that it is rare to see in collections anything 

 but the denuded skeleton of the colony. In Antipathes arborea, the 



