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THE ANIMALS AND MAN 



a body of quite different appearance. It corresponds in 

 general to an umbrella or bell (fig. 56), around the edge 

 of which are disposed numerous threads or tentacles (cor- 

 responding to the tentacles of the polyp). The mouth- 

 opening is at the end of a longer or shorter projection which 

 hangs from the middle of the under side of the umbrella, 



FIG. 56. A jellyfish or medusa, Gonionema vertens, eating 

 two small fishes. (Natural size.) 



like a short, thick handle. The body-cavity, or primitive 

 stomach, extends out into the umbrella-shaped part of the 

 body. By alternately clapping shut and opening the um- 

 brella the jellyfish swims about. 



Jellyfishes occur in great numbers on the surface of the 

 ocean, and are familiar to sailors under the name of "sea- 

 blubs." Some live in the deeper waters; a few specimens 



