COELENTEEA (JELLY-FISHES, CORALS, ETC.). 43 
COELENTERA 
The rest of the Gallery is occupied by the fossil 
COELEXTERA (Hollovs^-guts). This great division of the 
animal kingdom, which comprises sea-anemones, corals, 
jelly-fishes, and their allies, owes its name to the fact that 
the body-wall of each individual encloses a single hollow 
chamber (not many as in sponges) which forms the digestive 
cavity of the animal, and is not traversed by any separate 
gut sucli as is found in echinoderms and all the other groups 
that follow. The body-wall consists of an inner and an 
outer layer of cells, the “ endoderm ” and " ectotlerm ” as 
they are respectively called, and between them a jelly-like 
layer, the “ mesogloea,” which is very thick and noticeable in 
an ordinary jelly-fish. In a jelly-fish, too, one may readily 
observe that the organs of the body are regularly ainanged on 
lines radiating from the centre (see Tig. 18). A radiate 
symmetry of this kind is found in most Coelentera. In 
many Coelentera the individuals or zooids unite to form 
colonies. 
Setting aside the Ctenophora, which some exclude from 
the Coelentera, and of which no fossils are known, the 
Coelentera may be divided into three classes: Hydrozoa, 
Scyphozoa, and Anthozoa. 
Tlie Hydrozoa include the fresh-water polyp Hydra, the 
Hydroid zoophytes such as Sertularia the sea-fir, the corals 
Millepora and Stylaster, and various forms without fossil 
allies. All of these have a simple tubular body-wall, 
enclosing a cylindrical cavity which is not divided by 
partitions ; the mouth is not pu.shed inwards ; the repro- 
ductive cells are derived from the ectoderm and are set free 
directly to the exterior. 
The Anthozoa (Flower-animals, also called Actinozoa 
or Rayed animals) include the sea-anemones, nearly all the 
stony corals, precious coral, sea-fans, sea-pens, and dead 
men’s fingers. In these the mouth is pushed inwards, so as 
to form a tube ; the body-cavity is divided by partitions, 
called mesenteries, which consist of mesogloea covered with 
endoderm; the reproductive cells are derived from this 
endoderm and are set free into the body -cavity whence they 
pass to the exterior through the mouth. 
The Scyphozoa (Cup-animals) comprise the larger jelly- 
fishes. Some place them with the Hydrozoa, which they 
Gallery X. 
Table-cases 
1 - 10 . 
Wall-cases 
1 - 6 . 
