CCELENTERATA : ACTINOZOA. 133 



for the separate polypes, which are always present in the latter 

 (fig. 44, a). The more important variations of detail which 

 occur in both classes of corals will be noticed under the differ- 

 ent families in which they occur. It only remains to add that 

 doubt has been thrown by eminent zoologists upon the validity 

 of the general distinction between sclerobasic and sclerodermic 

 corals, as above denned. 



Returning now to the Zoantharia Sderobasica, we find the 

 sub-order to contain the two families of the Antipathidce and 

 the Hyalonemadce, (or Hyalochcetida!). Of these the Arttipatkida 

 are chiefly noticeable because of their likeness to some of the 

 Gorgonidce, from which, however, they are readily distinguished 

 by the fact that the number of their tentacles is a multiple of 

 six, whereas in the latter it is a multiple of four. Antipathes 

 itself (fig. 45), possesses a horny sclerobasic corallum, which may 

 be simple or branched, and is covered with numerous small 

 polypes, united together by a ccenosarc, and possessing six 

 tentacles each. 



Fig- 45- P art f a living stem of Antipathes an^uina, of the natural size. 

 (After Dana.) 



The second family, that of the Hyalommada, contains the 

 so-called " Glass-zoophytes," the true nature and position of 

 which has been a subject of much controversy. By Dr Gray 

 the Hyalonemadce are believed to be true Actinozoa, and he 

 defines them as follows : " Social Zoanthoid polypes secreting 

 a central, siliceous, internal, axial coil for their support. The 

 upper half of the coil covered by a uniform cylindrical bark, 

 regularly studded with retractile polypes." The lower portion 

 of the siliceous rope-ljfe axis, which looks exactly like a skein 

 of threads of glass, is sunk in the sand at the bottom of the 

 sea. The upper portion of the Hyalonema is often occupied 

 by a cup-shaped sponge, called Carteria, which Dr Gray 

 believes to be a parasitic growth. By Professors Loven, 

 Perceval Wright, Wyville Thomson, and others, the sponge 

 Carteria is looked upon as the true artificer of the siliceous rope, 

 and the polypes are regarded as paraskic, and as referable 

 to Palythoa. This last view, by which Hyalonema would be 

 placed amongst the siliceous sponges, appears, upon the whole, 

 to be most probably the correct one. In this case there is no 



