and is extremely impervious to water, 
Many 
Of wa 7 
species form stems 


more or less constant form 
by budding and branching, 
which are fixed to the ground 
or to Others 
single individuals, and are 
rocks. form 
then in most cases capable 
of free motion. In addition 
to increase by budding, we 
YX \ 
meet with sexual repro- 
\ 


duction, in which the egg 
A 
develops a microscopic larva, 
\\ 
swims about 
the 
takes some time to develop 
which 
\ 
freely 
with aid of cilia, and 
ATI 
into the mature animal. 
Alternation of generations is 
often met with, which com- 
bines the formation of stems 
with the alternation of sexual 
and asexual reproduction 
This makes the life-history 
of many Ca/lenterata very 
are 
complicated. Sponges 
used in our household eco- 
nomy; but of far greater 
importance in Nature are 
: Urticating Capsule. 
some of the corals, which eae 
% a. Scare) Thread rolled up; 2) ditto, half 
build up w hole mountains unfolded; 3) ditto, fully unrolled. 
and islands. (Highly magnified.) 

60 
The Calenterata are divided into four classes, 
the first three of which are remarkable for the pos- 
session of urticating organs. These are micrcscopic 
Weapons consisting of an oval capsule filled with 
fluid, containing a hollow spiral thread. The least 
touch bursts the capsule; when the thread darts out, 
unwinds, and fixes itself with the hairs and bristles 
which invest it, in the skin of the victim. 
it armed causes violent 
tion, powerful enough to cripple small animals, and 
the more they struggle, the more poisoned arrows 
them. The number of these microscopic 
weapons is enormous, for a single tentacle of Anthea 
cereus has been estimated to contain 43 millions. 
The venom 
with which is inflamma- 
pierce 
All these animals are marine, with a few un- 
important exceptions; and they are divided as follows: 
Class I. Ctenophora. 
Class I]. Polypomeduse. 
Order I. Acalepha. 
Il. Szphonophora. 
WI. = Hydroida. 
Class II]. Anthozoa. 
Order I. Octactinia. 
Il. Hevxactinia. 
Suborder {.  Actinaria. 
Il. Madreporaria. 
Class 1V. Porifera. 
Order I. Ceraospongia. 
Il. Halichondria. 
Hl. Calcispongia. 
Class |. Ctenophora. 
Freely-swimming animals of jelly-like consistence. | no alternation of generations. 
The mouth, which is often surrounded by lobes 
and tentacles, leads to a body-cavity. There ara 
8 zones of plates, bearing cilia, which run from 
one pole of the body to the other, on the upper 
surface, and the animal moves by the combined 
action of the cilia, and by the contraction of its 
body. The animals are hermaphrodite, and there is 

They feed on other 
marine animals. — Three species are represented on 
Plate XXIX; Fig. k. Beroe ovata; fig. 2. Cestum Veneris, 
a ribbon-shaped transparent creature, which shines in 
the sun with the most beautiful colours when swimming 
in the sea; and fig. m. Cydippe pileus, a rounded 
species, with two long retractile filaments which it 
uses to catch its prey. 
Class Il. Polypomeduse. 
Here we meet with an assemblage of creatures 
which do not seem to have the slightest resemblance 
between them, such as the jelly-fish and the sea- 
anemones. And yet these forms are so closely allied 
that it can only be supposed, that one has origi- 
nated from the other. Here, too, we meet with alter- 
nation of generations. The Meduse, or Jelly-fish, 
are sexually-mature animals, but their eggs do not 
produce jelly-fish. The young animal fixes: itself 
firmly, and grows to a branching tree, which is 
called a polyp or polypidum. Young Medusz are 
produced on the branches of this tree, which detach 

themselves, swim about, frequently grow much larger, 
and again reproduce themselves sexually. This is 
the rule, though we meet with exceptions in some 
subdivisions. Among the lowest forms, the Meduse 
do not detach themselves from the polypidom, but 
produce eggs, so that they sink from the level of 
independent beings to that of mere organs. In the 
higher forms, the reverse is the case. Here the 
Medusa-stage is greatly developed, and the polyp- 
stage much reduced, for the polypidom does not 
branch, while the Medusz are detached by con- 
striction. 
