The third have ordinary tentacula, occurring in great numbers like tassels or tufts around the mouth; their integument is either hardened into stone, or becomes fleshy, as in the Star-corals and Actiniæ.
3474. There is no doubt that the naked Polyps are closely allied to the Infusoria, and among them indeed to the Rotifera, so that they represent but a higher stage of these creatures, characterized by superior size and by tentacular in place of ciliary or vibratile hairs.
3475. The Cellulariæ cannot be more distinctly characterized than by saying that they are cortices or ramules inhabited by Vorticellæ. Thus they are Vorticellæ surrounded by a shell, and may be compared to ova, in whose coriaceous or leathery shell calcareous granules are blended, as in the eggs of the Crocodiles and Tortoises.
3476. They increase by means of ova and by ramification, if the former mode of division is not carried too far.
3477. The tubes of the Tubulariæ appear to be nothing else than the posterior extremity of the Polyp, desiccated or dried. These tubes are not therefore the product of an excretion, but the body itself.
3478. On the contrary, the tubes of the Sertulariæ must be held as being a tegumental excretion, within which the Polyp ramifies and produces ova-cysts. If the naked Polyps resemble ova which are devoid of shells, such as the roe or spawn of Fishes, then the Sertulariæ resemble ova surrounded by a tough skin, like those of Rays and Serpents.
The Radiated Polyps or Horn-corals are invariably ramified and converted towards their interior into a common horny or stony mass; so that the animals themselves appear to have coalesced upon this into a common tegument or bark. They possess a stomach and ovaries surrounding it, which open into the border of the mouth between the rays. They thus increase by ova and ramifications.
They therefore represent the class proper of the Polyps.
The tufted Polyps comprise the proper Corals or Lithozoa, are in form and substance like the Acalephæ but with this difference, that the covering is mostly lithoidal, while in many Acalephans, as the Porpitæ, it only appears as a cartilaginous disc or plate.
3479. These Corals are true ova, having a perfect calcareous shell, like that of the Bird. The gelatinous animal which adheres within a wide-mouthed Madrepore, e. g. Fungia, resembles a vitellus just hatched, and from which the fœtal envelopes have been developed.