NORTH ZOOL. GAL,] NATURAL HISTORY. 131 
nevertheless cannot be confidently pronounced to belong 
to the animal, rather than to the vegetable kingdom. 
In some, the skeleton, which alone can be shewn in the 
dry state, consists of a horny fibre, ( Spongia ,) in others it 
is formed of interwoven calcareous spicula, which greatly 
vary in their shape. In a few the spicula are formed of pure 
flint, and of sufficient hardness to scratch glass. 
The Tethya , (Table 7,) differs from the sponges with 
siliceous spicula in being more or less globular, with all the 
spicula radiating from the centre, and in its outer surface 
being covered with a crust formed of minute calcareous 
globules. 
ROOM II. 
The Table Cases in the Secondand Third Rooms con¬ 
tain the collection of Radiated Animals, ( Centronice , 
Pallas,) so called from all the parts of their body and 
members being disposed in a radiated form, which often 
gives them the shape of the flowers of plants. 
The pores of the skin of some kinds, and the whole of 
the cellular substance of others, is often so filled with 
calcareous matter, as to leave, when the animal is dead or 
removed, a hard case or a stony coral ; the latter often 
representing, in a very perfect manner, all the more import¬ 
ant characters of the animal. It is the hard parts or 
skeletons, as they may be called, of these animals, which 
alone can be shewn with any effect in collections, but 
whenever it is possible they should be studied in connec¬ 
tion with the animals which form them, as the animal 
alone affords the proper characters for their classification, 
and the study of the animal and coral together, enables 
the student to understand, in other cases, by the exa¬ 
mination of the coral alone, what was the probable 
structure of the animal that formed it. 
The Table Cases of the Second Room contain the 
hard parts of the Echinodermata, so called from their 
body being covered with a hard coat formed of variously 
shaped calcareous pieces imbedded in the surface of the 
skin. These pieces are formed by the earthy particles 
being deposited round certain definite spots in the 
skin, and as they are developed, they assume a definite 
arrangement into certain distinct shapes peculiar to the 
different kinds ; although these are strongly united to- 
