122 MANUAL OF ZOOLOGY. 



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

 doubt hias been thrown by eminent zoologists upon the valid- 

 ity of the general distinction between sclerobasic and sclero- 

 dermic corals, as above defined. 



Returning now to ^^ Zoantharia Sderobasica, yf& find the 

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

 the Hyalonemadm (or Hyalochxtidai). Of these the Antipathidm 

 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 possesses a horny sclerobasic corallum, which may be 

 simple or branched, and is covered with numerous small 

 polypes, united together by a coenosarc, and possessing six 

 tentacles each. 



The second family, that of the Hyalonemadtz, contains the 

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

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

 the Hyalonemadm 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-like 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 parasitic, and as referable to 

 Palythoa. This la§t 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 

 Actinozoon, as far as is yet known, which possesses the power 

 of secreting a siliceous skeleton, in this respect presenting a 

 striking contrast to the Protozoa. 



Sub-order III. Zoantharia Sclerodermata. — The mem- 

 bers of this sub-order include the great bulk of the coral-pro- 

 ducing or " coralligenous " zoophytes of recent seas. They 

 are defined by the possession of a sclerodermic corallum, the 

 parts of which are arranged in multiples of five or six. The 

 actinosoraa may be simple, consisting of a single polype, or it 

 may be composite, consisting of several polypes united by a 

 coenosarc. 



