60 ACALEPIIS IN GENERAL. Part I. 



might have satisfied any imprejudiced investigator tluit they are not Polyps, nay, 

 not even Radiata, but a kind of low Mollusks.^ 



What are commonly called Corals are communities of individuals possessing a 

 solid frame, but of the most heterogeneous structure, and having no conmion 

 character except the solidity of their frame. The moment we take into account 

 the anatomical structure of the beings forming such communities, we must distinguish 

 several kinds of Coral stocks. First, those which are uniforndy calcareous, formed 

 by genuine Polyps allied to the Actinia?. In flict these Coral stocks differ from 

 the Actinite only by the j^resence of solid deposits in the walls of their body. 

 Such are the Astra\ins and Madrepores, all of which have, like the Actinia^, numer- 

 ous simple tentacles, and a digestive cavity hanging l)eIow the mouth, as well as 

 radiating partitions iirojecting into the main cavity of the l)ody, and to which the 

 ovaries and sj^ermaries are suspended. Secondly, on account of the similarity in 

 the organization of their individuals, we would unite, as another grt)up of Corals, 

 the various solid stocks formed by Halcyonoid Polyps. Some of them are calcare- 

 ous, like tlie Actinoids, the Red Coral, for instance ; others are horny, the Gorgonia? ; 

 and others consist of calcareous tubes, such as Tubipora. The Corals of these Ilal- 

 cyoiroid Polyps are, it is true, far more diversified than those of the Actinoids, though 

 there seems to be much less difference between the animals themselves than among 

 the latter. They all have eight fringed tentacles, and agree fully in this respect, as 

 well as in their general structure, with those Halcj'onoids which have no solid 

 frame at all, as the genera Halcyonium and Renilla, or only a simple horny rod 

 in their axis, as Virgularia and Pennatula. 



On account of the special homologies of the Actinoids and IlalcA'onoids, there 

 can lie no doubt that these two types of Polyps Ijelong to one and the same 

 natural group, as Dana has first shown. They all have vertical radiating partitions 

 dividing the main cavity of the body into chandlers, which connnunicate freely 

 with the cavity of the tentacles ; in all, the ovaries and spermaries are found 

 hanging freely from the free inner edge of these partitions, and in all there is 

 a distinct digestive sac suspended in the upper jiart of the main cavity of the 

 body. They are, in one word, strictly homologous to the Actinitv;, the structure 

 of which we have considered more fully above. 



Among the Stony Corals generally referred to the Actinoid Polyps tliere is one 



^ Siebokl in his Toxt-book of Comparative Aiiat- has not jet b(?en founil. Fuit, siiivly, hUateral 



omy, and Kiilliker in his Schwimmpolypen, refcrriMl animals with an aUmenfary canal i)\im at both 



to above, (|). 27, note 12,) still unite tlie Lryozoa with extrrmities and bent in a plane dividing the body 



the Polyjis. KoUiker is partieularly explicit on that into equal halves ran no longer be associated with 



point, and believes that the expression by whieh Polyps, which are built upon a plan characterized 



Molhisks and Radiates may be clearly distingui>lied by radiation around a vertical axis. 



