CLASS V. POLYPI: ORDER 3. HYDROIDA. 641 
RED CORAL. THE SEA-PEN. 
Coral^ a substance of great beauty, and of considerable value. It appears to be confined to the 
Mediterranean Sea, where it grows, especially on the southern coast, attached to rocks at consid- 
erable depths in the sea. It is fished up from the deep by means of nets and other instruments.. 
The manufacture of ornaments of this coral at Naples is of great extent. 
THE PENN^TULID^. 
The zoophytes of the preceding groups all grow attached by the base to rocks or other sub- 
marine bodies ; in the present family, on the contrary, the polypidom is completely unattached, 
and is only retained in its proper position by the insertion of the lower portion into the sand 
or mud of the bottom of the sea. The main stem of the polypidom of these animals is 
fleshy, but is furnished with an internal bony axis, which, however, does not reach to either ex- 
tremity of the stalk. The polypes are not situated upon this portion, but upon a series of 
lamellae, Avhich stand out upon each side of the stalk, giving the whole polypidom, in some cases, 
the appearance of a large quill-feather. Of this the Sea-Pei^, Pennatula grisea, is a famihar ex- 
ample. There are, however, many other forms. 
ORDER 3. HYDEOIDA. 
This order contains some of the most wonderful of known animal existences. The body gen- 
erally consists of a homogeneous aggregation of vesicular granules, held together by a glairy, inter- 
cellular substance, and capable of great extension and contraction, so that the creature may at 
pleasure assume a great variety of forms. The larger number of these animals hve in societies, 
with branched horny polypidoms. 
THE HTDEAID^. 
This family contains only a single genus, Hydra^ some species of which may be met with in 
almost every piece of stagnant water. Tliey are generally attached to some aquatic plant, the 
animal consisting of a long gelatinous cylinder, furnished with tentacles, with which it stretches 
about in the water for its minute prey. When contracted it becomes a mere lump of jelly. The 
Vol. IT,— 81 
