CLASS V. POLYPI. 
635 
fleet as this, seen with the sun shining strongly upon them, is a magnificent spectacle, from 
' ^"^^ tlie beautiful iridescence with which the sunlight is 
reflected to the eye of the beholder. With the ap- 
proach of night this scene of beauty only gives place 
to another ; for these Medusae are exceedingly lumi- 
^ nous in the dark. 
The Medusa aurita, Pelagia Labiche, and Cyanaea 
ca^yillcita, which we have already noticed, belong to 
this order, as well as a multitude of others. 
ORDER 2. GYMNOPHTHALMATA. 
This order includes a great number of genera, the 
species of which vary exceedingly in form and size- 
Several species are found in the European seas, and 
among them the Sarsice and Lizzice, some of which we 
have mentioned ; also those of the genus Thauman- 
tias, which are most important agents in producing the 
luminosity which is often witnessed in those parts of 
the ocean. The Oceanidce are among the most delicate and beautiful of the order, consisting of 
a conical or globular glassy body, within which a variously colored peduncle may be seen. In 
the genus Turris the tentacles are exceedingly numerous, while in Saj^henia they are reduced to 
two. In the Willsidce, the radiating vessels, six in number, are curiously forked, and there are 
.six ovaries placed round the base of the stomach. The ^quoridce include some of the largest 
of the naked-eyed Medusae. 
THE EHIZOSTOMA CTJVIEEI. 
This class, deriving its name from the Greek, 2^olus, many, andj-^^oMs, a foot, includes a great num- 
ber of animals, bearing the various names of Sea- Anemones, Corals, Madrepores, Zoopliytes, Coral- 
lines^ &c. Most of them are of very simple construction. They are all aquatic in their mode of life, 
and by far the greater number inhabit the sea, a 
very few only being found in fresh water. Most of 
them live in societies of greater or less extent, sup- 
ported on a common stock, or jmlypidom, a word 
which means the House of the Polypi, this being 
sometimes horny, sometimes calcareous. The little 
creatures are either imbedded in cavities, formed im- 
mediately in the substance of this support, or in a sort 
of flesh which sometimes incrusts it ; or they are in- 
closed, as in the horny polypidoms, in minute cups 
or tubes, from which the body can be protruded at 
pleasure, and again retracted at the approach of 
danger, or during repose. These social polypi are 
always of small size, although the structures pro- 
duced by the united labors of successive multitudes, 
are often sufiicient to produce important changes even 
in the face of nature. Many of the solitary species, 
however, attain a considerable magnitude. The 
bodies of these animals are generally cylindrical in 
form, with a fringe of tentacles, or arms, frequently consisting of a considerable number, sur- 
rounding the anterior extremity, in the center of which the mouth is situated. The mouth is 
POLTPIDOM OF TREE-CORAL. 
