INTRODUCTION. XXV 
size; particularly as when the first set of polypi die, their 
cells remain to be increased by the next generation. The 
sea-mat, or floster, is a specimen of these animals. The ra- 
diated polypi are divided into three orders, which are thus 
named and characterised. 
1 . HeliantJioida. Some naturalists include in this order the actinia, 
or sea-anemone ; but all agree that it contains the animals of 
the madrepores, sea-mushrooms, and brainstones, which live 
in communities, and possess the power of secreting calcare- 
ous matters, which they emit to form these stony substances. 
2. Asteroida. Some of the animals belonging to this division are 
called sea-pens, and others form some of the different kinds 
of coral, particularly that used for necklaces, &c. 
3. Hydroida. This order includes the fresh-water polypi, which 
it is well known, by the experiments that have been tried, 
may be cut in pieces and even turned inside out with- 
out destroying life. The Lithophytes are divided into two 
families, viz., those covered with a thick jointed crust, which 
are the coral insects, or Corallines of Linnaeus ; and those called 
by De Blainville Fucoidece, which closely resemble sea-weeds. 
The Sponges differ so much from the other zoophytes, that they 
have been formed by De Blainville into a separate class, 
under the name of Amorphozoa. The sponge, in its native 
state, appears to be filled with a kind of jelly, but when ex- 
amined with a microscope, this jelly will be discovered to be 
full of transparent spherical granules, which are small animals. 
Sometimes sandy or calcareous particles are found in sponge, 
as though it were on the point of being changed into a 
polypidom. 
V. The Infusoria, or Animalcule, are so small as to be invisible to 
the naked eye, and they are all inhabitants of liquids. Cuvier 
arranged them in two orders, one of which he called Les 
Rotiferes, and the other Les Infusories homogenes, but by 
Lamarck's system, which is now generally followed, the first 
of these divisions is now included in the polypi ; and the 
latter are divided into two orders, one with external organs and 
the other without. The great number of these animals and 
their singular forms must be present to the mind of every 
one who has seen a drop of stagnant water magnified in a 
powerful microscope. 
