ORDERACTINOIDEA. 45 



clusters are attached in a corresponding manner to the margin of the 

 ovarian lamella?. The ovules, though sometimes retained in the cavity 

 till they are developed, generally pass out before, and, in either case, 

 escape takes place through the stomach and mouth. 



The similarity between these animals and tlie Hydroidea is hence 

 very close. The localisation of the genital functions in distinct organs 

 appears to be the character upon vi'hich their principal diflferences 

 depend. The relation of the visceral cavity of these animals to the 

 tubular axis of the Sertularia is obvious. Though extremely short in 

 the Actinia, we find it several times longer than the stomach in the 

 Zoanthidse, and still longer, and taking the form of a slender tube, in 

 the Tubipora? and Alcyonia. 



Subdivision of the Actinoidea. 



39. The facts considered lead to a natural subdivision of the group 

 Actinoidea. In the Actinia and Palythoa the tentacles are numerous 

 and naked, and have a puncture at apex, while, in the Tubipora 

 and allied species, these organs are but eight in number, and are 

 fringed with papillae, each with its minute puncture, and none at the 

 extremity of the tentacle. The Actinoidea are hence naturally subdi- 

 vided into the two following groups : 



I. AcTiNARiA. — Tentacles, {with few exceptions,) naked or not papil- 

 lose, six, twelve, or more in number. This division includes the Actinias, 

 Madrepores, Astreeas, &c. (The cells in the coral-making species are 

 more or less perfectly radiate within.) 



II. Alcyonaria. Tentacles fringed with papillce., eight in number. 

 This divi.'^ion includes the Tubipores, Gorgonias, Alcyonia, &c. 

 (The cells of the coral-making species are never radiate or striate 

 within.)* 



* The fact that in a compound Alcyonium the tubular visceral cavities of the several 

 polyps branch from one another, with a free intercommunication, has been considered as 

 widely separating the Alcyonaria from the Actinaria. In the Tubipora: among the former, 

 however, this connexion is not more perfect Ihan in the Zoanthidee, and the same is true 

 of the young state of the polyp-bud in many species. The seriate polyps in a Meandrina 

 have even a more open communication, and in some of the compound Fungidte adjacent 

 polyps have scarcely any thing but a mouth that can be said to be private property. The 

 peculiar character of this connexion between polyps in certain Alcyonaria merits notice, 

 but not the importance which has been attached to it. 



12 



