50 ZOOPHYTES. 



larger cells, they are nearly equal; while in the latter, half are obso- 

 lescent. In the Merulinas, there are seven or eight larger lamellae to 

 a fourth of an inch, with three or four intermediate nearly obsolete, 

 making in all ten or eleven in this breadth. The same is generally 

 true of the Euphylliae and Meandrinse. In the Mussse, much larger 

 species, there are seven or eight to a fourth of an inch, as in the 

 Actinia marginata ($ 25), and half of these are quite small or obso- 

 lescent. It appears, therefore, that the number varies, in different 

 species, from seven to fifteen. The last number is seldom exceeded, 

 yet instances of this are found in some Meandrinas and many of the 

 attached Fungidse. 



II. ALCYONARIA. 44. The simple polyps, among the Alcyonaria, 

 have a great similarity throughout. The number of tentacles being 

 fixed, there is not room for the same diversity of form as in the Acti- 

 naria. The principal varieties in external appearance proceed from 

 variations in the length and position of the papillae. These appen- 

 dages to the tentacles are sometimes quite long, and give a graceful 

 delicacy to the flower, scarcely exceeded in the vegetable kingdom.* 

 Usually, they form a short fringe in two or three series on either side 

 of the rays, as shown in the Tubipora, already described.! In one 

 of the species of this genus (T. syringa), they are so evenly laid 

 together that the fringe seems to be wanting. In one of the Xeninse, 

 found at the Feejee Islands,! the papillae are minute wart-like pro- 

 minences, scattered over the surface of the ray. Each little promi- 

 nence has the minute puncture at apex, which is characteristic of the 

 Alcyonia group. 



II. SECRETION OF THE CORALLUM IN THE ACTINOIDEA. 



45. The corallum has been described as in general an internal 

 secretion, formed within the polyp, and not a covering enclosing the 

 same, as in the Mollusca. We may examine more particularly the 

 mode of its secretion and its relations to the animal. 



There appear to be two kinds of coral secretions among the Acti- 

 noidea : 



1. Secretions formed within the animal which are mostly calcareous. 



* See plate 59, figure 3. f See plate 59, figures 1,2. | See plate 57, figure 2. 



This character of these secretions was first pointed out by Ehrenberg, in his Memoir 

 on the Corals of the Red Sea, in the Transactions of the Berlin Academy, for 1832. 

 Since then, they have been more fully explained by Milne Edwards, in the Annales des 

 Sciences Naturelles, for 1838, x., 2d series, 321. 



