Growth J and Habits of Coral Zoophytes. 45 



division of zooph^'tes, not yet touched upon, and also to the 

 Hydroidea and Bryozoa, which are likewise coral-making 

 animals. 



The Alcyonoidea. — The polyps of the Alcyonium* group of 

 zoophytes differ from those which have been occupying us, in 

 having but eight tentacles, and these are fringed with minute 

 papillae. The organ-pipe coral (Tubipora), is of this kind. 

 When expanded in the sea, a clump resembles a bed of pinks, 

 or looks like a lilac-cluster that had been dropped in the 

 water ; and this resemblance extends to the colour and size 

 of the flowers as well as their form. 



Some of these zoophytes secrete lime and form a tube ; and 

 of this kind is the Tubipora. Others secrete only scattered 

 granules of lime through the tissues ; and still others are 

 fleshy throughout. Many of them, besides forming granular 

 calcareous secretions within the body of the polyp, give origin 

 to a horny secretion at base, analogous to the epidermic se- 

 cretions (hair-nails) of other animals ; and this secretion 

 receiving constant additions from the polyps as they are suc- 

 cessively budded out, forms the axis of the growing branch. 

 Of this character is the horny axis of the Gorgonia or sea- 

 fan, which was long taken for a vegetable production. The 

 crust which covers the axis consists of united polyps, which 

 expand over its surface ; and when expanded, each branch 

 becomes a spike of flowers. 



The Hydroidea. — The Hydroidea include the groups Hy- 

 dra, Sertularia, Tubularia, and the allied. Some species form 

 thready tufts and plumes of extreme delicacy, and others 

 (the Hydrae) are simple polyps. The fine branchlets of the 

 feathery species consist, when dead, of one or two series of 

 microscopic cells arranged like tiny cups, tubes, or goblets, 

 along the stem ; and when alive, each cell is the site of a 

 minute flower animal. A coronet of tentacles surrounds the 

 mouth, as in the actiniae, though somewhat difi^erent in cha- 



* This name is derived from Alcyone, the fabled daughter of Neptune, and 

 although from a Greek word, having the aspirate breathing to the first letter, 

 it was written by the Latins as here (and by Linnaeus and others), without 

 the H, 



