94 JOURNAL OF MARINE ZOOLOGY AND MICROSCOPY. 



consists of small, strong-spiked straight rods suo-in. long. Most 

 peculiar forms are sometimes assumed, due to the great and irregular 

 development of the spines ; being sometimes broadly bilobed, some- 

 times even trificl. (<?) In the interior of the colony, in the stiff 

 mesoglcea that divides and yet joins the different polyps, scattered 

 spicules, very slightly spined, and nearly straight, occur ; while a 

 fifth form of spicule (d) occurs in the thick wall of the oesophagus. 

 These last are the smallest of any in the colony and barely measure 

 s ott -in. long. 



In Al&yoniurn digitatum, the spicules differ very charac- 

 teristically from all the preceding, in their much greater profusion, 

 in their greater massiveness, and in their peculiar shape. The rod- 

 like form, so closely adhered to in A. palmatum, is here nearly 

 obliterated, and the spicules are often irregularly branched, and all 

 the limbs beset by enormous wart-spines. (Fig. 3). 



In the Organ-Pipe Coral (Tubipora) the spicules of the mesoglsea 

 surrounding each individual, become locked firmly together by 

 numerous minute serrations, and form perfect calcareous tubes. In 

 the Reel Coral of commerce, (Cor allium rubrum), on the other 

 band, a strong central stony axis is formed by an even more intimate 

 association of the spicules of the axis of the colon}?, due to an actual 

 cementing together of these tiny limy rods. In Tubipora the polyps 

 can retract within their protective tubes, but in the Red Coral 

 there is scarcely any provision for the retraction, for safety, of the 

 polyps. 



As in the Anthozoa generally, so in Alcyonium the sexes are 

 separate ; indeed even the sexes of different colonies are distinct ; 

 the individuals in any one commonwealth are thus either all males, 

 or else all females. The ova and the sperm masses are borne on 

 little stalked capsules upon the free edges of the mesenteries, and 

 development takes place outside the parent. The embryos are free 

 swimming by means of a complete investment of lashing threads 

 or cilia ; a little while they sport thus amid the waves, and then 

 affix themselves to some rock, and by continued budding produce 

 •extensive colonies. 



Note the very large size of the hollow pinnate tentacles, and the 

 thickness of the walls of the oesophagus (st.) Below the latter, the 

 upper parts of the mesenteries are very apparent because of their 

 greatly convoluted and thickened margins (PL x, Fig. 1, m. /.) ; from 

 this point downwards, the mesenteries decrease ra]3idfy in jjrominence, 

 and soon show us very slight ridges only. The two dorsal ones 

 are of greater length than any of the others, i.e., descending lower 

 down the gastric cavity, and whereas their thickened edges or 

 mesenterial filaments (eraspecla) are composed of strongly ciliated 



