ACTINOZOA. 209 



ally seen to become exquisitely pellucid, while 

 from all parts of its surface numbers of tiny 

 polypes, emerging, expand to the utmost their 

 star-shaped crowns of delicately fringed tentacula. 

 Within the somatic chambers circulating currents 

 may now be observed. These find their way up 

 one side of the tentacles, following the course of 

 the several fringes, and, having gained their sum- 

 mits, again revert, proceeding in a contrary direc- 

 tion. So that here, as in many Zoantharia, it 

 would not, perhaps, be too much to say that the 

 tentacles, by reason of the delicacy of their ciliated 

 walls, fulfil the proper function of a respiratory 

 system. 



In Sarcodidyon, as in Alcyonium, a spicular 

 corallum occurs, but the coenosarc is scanty and 

 creeping, resembling that of the Zoanthidce. So 

 also in Cornularia, the corallum of which is, 

 however, more consolidated. But of all the Al- 

 cyonidcG proper Telestho, with its tufted, sub-cal- 

 careous, tubular corallum, makes the nearest 

 approach to the allied family of Tubiporidce. 



The beautiful Organ-pipe Corals, forming the 

 several species of the genus Tuhipora, appear to 

 be the sole representatives of this group. Allusion 

 has already been made to the exceptional structure 

 of their corallum, the colour of which, in all cases, 

 is of a bright crimson-red. The polypes are 

 either violet or grass-green in tint, and, according 

 to the dissections of Dana, present this anatomical 

 peculiarity, that two only of the mesenteric edges 

 are furnished with ova, the remaining six sup- 

 porting spermaria. The oral extremity of each 

 polype can be inverted for protection into the 

 summit of its calcareous tube, but it is wrong to 



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