134 
NATURAL HISTORY. 
[n. ZOOL. GAL. 
the genus Alcyonidium , the outer skin is thick and cartilaginous, form¬ 
ing, when the animals are united together, a hard fleshy mass, which has 
been mistaken for an alga , and is difficult to keep in a dry state. In 
others, the skin is more or less transparent and horny, so that the mass 
assumes much of the appearance of Sertularia, as in the genera Seria- 
laria , &c., (Case 31,) but in general the skin is more or less rapidly 
hardened into a stony case, according to the manner in which the ani¬ 
mal is reproduced either by the spontaneous division of its body, or by 
the emission of buds from various parts of its surface, and these differ¬ 
ences produce very differently shaped corals. 
Sometimes the mass of animals assumes the form of a leaf-like 
expansion, attached by its lower surface to shells and other marine 
bodies; then the younger animals are formed on the circumference of 
the mass, and if the surface of the coral is examined, it will shew all 
the extraordinary and different changes which the skin assumes as the 
animals which formed it increase in age; the skin of the younger 
animal being thin and soft, it gradually becomes harder until the animal 
arrives at its perfect state of developement, and then it thickens, blisters, 
and swells until the hole through which the head of the animal was 
emitted is obliterated, and the animals are destroyed by the de¬ 
velopement of their own skin. These cells are to be found gradually 
spreading from the centre of the expansion or the base of the stem of 
the more tree-like coral, while the new animals and their cells are being 
developed on the edge of the frond or the tips of the branches. Some¬ 
times, as the mass increases in size, it sends up more or less erect lobes, 
and if these lobes have both of their sides equally exposed to the in¬ 
fluence of the sea and light, so that the animals of each side can 
procure their nourishment, then they form two layers of cells applied 
back to back, as in Eschara. Sometimes the new cells are formed on 
the surface of the older and dead ones, so as to form a cylindrical 
branched coral, having all the new pores developed at the ends of the 
branches. 
The upright Cases on the Table Cases are intended to 
contain the large specimens of the skeletons of Zoophytes, or Corals, 
arranged in the same manner as the more complete series in the Tables: 
and the collection of these animals preserved in spirits, (especially 
those which cannot be well exhibited in a dry state,) is kept in the Wall 
Cases of the Fifth Room of this Gallery. 
The following is a continuation of the Catalogue of the genera of 
radiated animals, (from page 119.) The numbers appended indicate 
the Table Cases in this Room which contain the specimens in the 
collection. 
Section II. 
Leiodermata. 
Class III. 
Ac ALEPH A. 
Order I. Phanero- 
CARPiE. 
Fam. I. Rhizosiomi- 
drn. 
2. Medusidcs. 
Order II. Crypto- Fam. 3. Callianiadee. Porpita, 1. 
carp^:. Order IV. Physo- Class IV. 
Fam. 1. Geryorddce. grad as. Zoophyta. 
2. Ocean idee. Fam. 1. Diphyidee. 
3. Mquoridee. 2. Physopho- Order I. Zoantha- 
4. Berenicidce. ridee. RIA» 
Order III. Cilio- Order V. Chondro- Fam. 1. Actiniadce. 
GRAD2E. GRAD2E. Act i n i a . 
Fam. 1. Beroidee. Fam - 1 * ^lelhdee. Anthea. 
2. Mneineidee. Velelia, Case 1. Metridium. 
