XXIV INTRODUCTION. 
is now generally followed, divides them into three orders, 
viz. 
1 . The Fistuloides, or Holothurida, which have cylindrical bodies, 
leathery skins, and mouths surrounded by tentacula, 
These creatures live in the sea, or in the sands on the sea- 
shore ; and the trepang, or eatable worm of the Chinese, is 
one of them. 
2. The Echinides. These are the sea-urchins, properly so called, 
and the shells, when the animals are out of them, are called 
sea -eggs. The Echinides live in the sea, and they have long 
arms to secure their prey, and two series of bone-like teeth 
to crush it. They lay eggs, and the roe, or imperfect eggs, 
occupy a large portion of the space within the shell when 
the animal is still alive. 
3. The Stetterides, or Asterias, are the star-fish. The mouth in 
these creatures is in the middle of the lower surface, and it 
has a membranous lip, capable of great dilation, but furnished 
with angular projections for capturing and crushing its prey. 
The skin is soft but leathery, and it is covered on the back 
with spongeous tubercles or scales. The rays are hollow 
beneath, and furnished with tentaculae, by the aid of which 
the star-fish manages to crawl backwards, forwards, or side- 
ways, as the case may be, any of the rays serving as a leader. 
These animals are found on the sea-shore, forming large beds, 
which are washed over by the sea. The Crinoidea, or stone- 
lilies, of which such curious fossil specimens have been found, 
are nearly allied to the star-fish. 
II. The Intestina, or Entozoa. The intestinal worms were divided 
into two kinds by Cuvier, viz. the Cavitaires, including the 
worms of children, the botts in horses, and other cylindrical 
worms ; and the Parenchymateux, or flat worms ; such as the 
fluke in sheep, and the tape-worm in human beings. 
III. Acalephee or Sea-Jellies. These creatures are of a soft and 
jelly-like substance, with a thin skin, and an unarmed 
mouth. There are two kinds, the Medusides, which have 
round bodies, and the Acalephes, the bodies of which are of 
an irregular shape. The Medusides are very numerous, 
and produce that beautiful phosphorescent light noticed by 
voyagers in the Australian seas. The most interesting of the 
Acalephes is the Portuguese man-of-war, or physales; and 
some naturalists include in it the actinia, or sea-anemone. 
IV. Polypes, or Anthozoa, according to Cuvier, were arranged 
in three orders, viz. the Polypes, the Lithophytes, and 
the Sponges; but to these Larmarck has added the Mol- 
luscous Polypes, calling the others the Radiated Polypes. The 
molluscous polypus is a very small animal. The mouth is 
wide and circular, and it is surrounded by a fringe of tenta- 
culae. This kind of polypi always dwells in a calcareous cell, 
which is so connected with its body that it cannot leave it. 
The crust, or shell, is called the polypidom, and as a number 
of polypi dwell together their polypidom soon becomes of a great 
