ACTINIAEIA. 181 



The space between this stomach and the outer envelope is divided 

 into eight equal compartments or cells by as many thin septa, ori- 

 ginating in a labial rim or lip between the basis of the tentacula, which 

 descend through the cylinder attached on the one side to the inner 

 tunic of the body, and on the other to the stomach, which is thus 

 retained in its position. 



The protruding portion of the polyp is very delicate, the internal 

 viscera being, as it were, enclosed in a bladder formed of two very thin 

 membranes in intimate union, so transparent as to permit a view of 

 their arrangement. At the base of the body, where thickest, it coalesces 

 with the base of the adjacent polyp ; thus constituting the common 

 cortical portion into which each animal retreats at will, by a process 

 in many respects resembling that by which a snail draws in its horns. 

 In the greater number of Asteroids this common portion secretes 

 carbonate of lime, which is deposited in the meshes of its tissues 

 either in granules or in crystalline spiculaB, which imparts a solid 

 consistency to the whole. The inner tissue meanwhile continues 

 unaltered, being prolonged throughout the polypiferous lining of the 

 cell, the abdominal cavity, and the longitudinal canals which permeate 

 the whole polyp, as well as the tubular net-work with which the 

 space between the canals is occupied. It is among these inner tissues 

 that the buds or gemmae are generated, by whose increase and evolu- 

 tion the polyp mass is enlarged, the shape and size depending on the 

 manner in which the buds are evolved ; for in some, as in the Pen- 

 natulidas, determinate spots only have the appropriated organization, 

 while in others, as in Alcyonium, the generative faculty appears to be 

 undefined and more diffused. 



THE ACTINIARIA. 



Here we leave the group of polyps which form united families. 

 The Sea Anemones, of which the Actinia are the type, consist of 

 Zoanthaires, which produce no corals, that is to say, of polyps 

 whose covering remains always soft, and in whose interior nothing 

 solid is produced. This order is usually divided into two families 

 the Adiniadse, having the tentacles in uninterrupted circles, with no 

 corallum, and the Minyadinse, having globose bodies, and very short 

 tentacula. 



