TYPES OF C@LENTERA—A SEA-ANEMONE. 
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Contrast between Medusoids (Hydromeduse) and 
Medusa (Scyphomedusa) 
Mepusorps. (CRASPEDOTA.) 
Mepusm&. (ACRASPEDA.) 
The majority are small ‘‘swimming- 
” 
A flap or velum (craspedon) projects in- 
wards from the margin of the bell. 
No teeniole, nor gastric filaments. 
A double nerve-ring around the margin. 
Naked sense organs either optic or audi- 
tory. hey are usually derived 
from the skin, but the auditory sacs 
may be modified tentacles. 
Reproductive organs on the radial canals 
or by the side of the manubrium. 
The reproductive cells are usually 
derived from the ectoderm. 
With the exception of the Trachy- 
medusa, all arise as the liberated 
reproductive persons of hydroid 
colonies. 
Many are large “ jelly-fish.” 
No velum. (The velarium of Aurelia 
is a mere fringe, very inconspicuous 
in the adult, and not inturned.) 
In the Scyphistoma there are four 
teniole, from part of which the 
gastric filaments of the adult grow. 
Eight separate nervous centres be- 
side the sense organs, and a sub- 
umbrellar nervous plexus. : 
Sense organs are modified tentacles, 
-and probably have almost always 
a triple function. They are usually 
protected by a hood. 
Reproductive organs in special pockets 
on the floor of the gastric cavity. 
The reproductive cells arise in the 
endoderm. 
Have no connection with hydroids, but 
may have a small sedentary polyp 
stage (or Scyphistoma) in the course 
of thei life history. 
Probably more nearly related to 
Anthozoa than to Hydrozoa. 
Fourth Type of CELENTERA.—A Sea-Anemone, such as 
Tealta crassicornis. Class ANTHOZOA 
Most sea-anemones live fixed to the rocks about low- 
water mark. All these fixed forms have a distinct basal 
disc, and may, like Zealia crassicornis, be half buried in 
sand and gravel; others, without a basal disc, are loosely 
inserted in the sand, e.g. Edwardsia and Certanthus. All 
are able to shift their positions by short stages. Some 
reef-anemones (Cvadactis) can crawl about on their 
tentacles. They feed on small animals — molluscs, 
crustaceans, worms—which are caught and stung by the 
tentacles. Many» depend on minute organisms; others 
may be seen trying to engulf molluscs decidedly too 
large for them. A few anemones, without pigment or with 
little, have symbiotic Algz in their endoderm cells; the 
bright pigments of many others seem to help in respiration. 
Besides the sexual reproduction (in which the young are 
