46 ZOOPHYTES. 
We glance at some of the principal varieties of structure in each of 
these divisions. 
I. Actinaria. 40. In one of the divisions of this group—the Anti- 
pathacea—the polyps have but six tentacles.* In the tentacles and 
the general appearance and habit of the polyp, they resemble the 
Madrepores, but no dissection has yet been made of them. 
41. The polyps of the Madreporacea, another division of the Acti- 
naria, are distinguished by twelve tentacles in a single series.| There 
is among them but little variety of structure. In a few species the 
alternate tentacles are of unequal size, and it is probable that the vis- 
ceral lamella have the same inequality : and in some Madrepores one 
of the tentacles is elongated and more flexible than the others :{ again, 
all are sometimes obsolete. 
The character of the cells formed by Madrepores show that in 
many of them two opposite interlamellar spaces in the visceral cavity 
are generally broader than the others, as in the Actiniz, and usually 
these two are very unequal. 
The only fleshy species known, which has the twelve tentacles of 
the Madrepores, is the Actinia clavus of Quoy and Gaymard,) found 
by them entangled in the tentacles of a Medusa, off the coast of New 
Holland. By their dissections, the stomach and visceral lamelle are 
shown to have nearly the characters of those in the Palythoa, except 
that the lamelle are equal and are twelve in number, corresponding 
to the tentacles. ‘The appearance of this Actinia expanded is very 
similar to that of a madrepore polyp. 
The most marked variation from the usual character of the Ma- 
dreporacea is found in the Porites family. In these the visceral 
cavity does not extend to the base of the animal, as in the other species 
of the group, and the visceral lamelle cannot be traced through the 
tissues of this portion. This structure is indicated by the porous coral 
secretions formed by this part of the polyp. Im external characters 
these polyps present few peculiarities. A few allied species (Gonio- 
pore) appear to have more than twelve tentacles, though all are in a 
single series, as in others of the Madreporacea. 
42. The polyps of the Caryophylha and Astrea tribes have more 
than twelve tentacles, and they are in two or more series or scattered. 
* Plate 56, figures 1 and 2. Tt Plate 31, figure 1. £ Plate 33, figure 1. 
§ Voyage de l’Astrolabe, iv. 150, pl. 10, figs.6 to 11. It is yet doubtful whether 
this species was actually an adult with its full number of tentacles. Several individuals 
were seen, which were about three-fourths of an inch long when expanded. 
