Chap. II. THE DIFFERENT RADIATA. 63 



types. The discovery that the Milleiwra is a geiinine Ilydroicl, and not at all 

 allied to the Actinoids, makes a farther revision of all these Stony Corals, the animals 

 of which have not yet been snfficiently investigated, particularly desirable. This 

 is especially the case with Pocillopora (PI. XV. Fig. 14''), which, from the structure 

 of the Coral stock itself, I am now satisfied, must also be referred to the Hydroids 

 with Millepora.^ I believe the same also to be the case with Seriatopora (PI. XV. 

 Figs. 15 and 15"). 



There is a fifth type of Coral stocks, still more remote in its structure from 

 the Polyps, which, as long as all Corals were considered to be Polyps, was, with 

 the rest, referred to that class. I allude to the so-called Corallines and the 

 Nullipores. When referring them to the Polyps, Lamarck assumed that there 

 existed animals of a very soft nature upon their surface ; which, however, could 

 not retreat into distinct cells, and therefore left no mark of their existence upon 

 the dried Coral stock. But since these Corallines have been more carefully ex- 

 amined, no trace of such animals has been observed ; and, to say the least, their 

 animal nature has become very questionable. For my own part, I entertain no 

 doubt, that, as the investigations of Decaisne^ first showed, they are neither more 

 nor less than genuine AlgJB with a tissue largely loaded with calcareous particles, 

 and may fairly be designated under the name of Limestone Algte. They are 

 true plants of the lowest type, forming, in consequence of the large amount of 

 lime they contain, Coral stocks of no small importance in the economy of the 

 Coral reefs. It is by their agencj', since they are capable of sustaining their life 

 even when not permanently under water, that the crest of the Coral reef is raised 

 above the level of low-water mark ; and the growth of some of their representatives 

 is so extensive that the exposed part of a large number of the islands of the 

 Florida reef is almost entirely composed of the fragments of these calcareous 

 sea-weeds. I have seen large slabs of rock, used in the construction of the foun- 

 dations of Fort Jefferson, upon the Tortugas Islands, composed entirely of the joints 

 of these calcareous searweeds, which were so distinct as to be recognized with ease. 



^ As the structure of the Coral stock of the - Decaisne (J.), Essais sur une classification 



Tabulata of Milne-Edwarils presents in all the same des Algues et des Polypes caleiferes, Ann. Sc. Nat. 



general features, it is highly probable that the whole 2de ser. 1842, XVII. p. 297. — Memoire sur les 



order will have to be referred to the class of Aca- Corallines ou Polypiers caleiferes, Ann. Sc. Nat. 



lephs. I am farther inclined to believe, that the 2de ser. 1842, XVIII. p. 96. See also Lindley, 



Eugosa will share the same fate. Their typical Vegetable Kingdom, London, 1853, 1 vol. 8vo. p. 



structure seems to be a combination of the char- 23. — Kutzing, Phycologia Generalis. — Harvey, a 



acteristics of Lucernaria and the Strobila state of Manual of the British Marine AlgK, London, 1848, 



the higher Discophora\ A section of Strombodes p. 103. Schweiger already refers the Corallines to 



recalls at once the appearance of a Strobila. the Alga>. 



