JELLYFISHES AND HYDROIDS 
A JELLYFISH is an umbrella-shaped creature with tentacles 
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and sense organs arranged at intervals around the outer edge 
of the umbrella, while the mouth and stomach occupy the position 
Fig. 8; 

PORTUGUESE MAN-OF-WAR. 
of the umbrella handle. 
This description apples 
well to the large jellyfishes 
called Scyphomeduse, but 
the smaller kinds called 
Hydromeduse have a deli- 
cate membrane extending 
inward all around from the 
umbrella-edge forming a 
diaphragm which partially 
closes the opening of the 
umbrella. Jellyfishes swim 
by rythmatically opening 
and closing their umbrella- 
like bodies. 
Jellyfishes are carni- 
vorous, feeding upon small 
fishes, crustacea, or one an- 
other. They capture their 
prey by means of their ten- 
tacles which are armed 
with thousands of little 
cells each containing a 
minute coiled tube so slen- 
der that it appears to be 
a mere thread. When ex- 
cited these cells burst, and 
the little threads are shot 
out with such force that they penetrate the skin of the victim, carry- 
ing with them a poison which quickly paralyzes a small fish. The 
