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THE ANIMAL KINGDOM 



Fiaure 10 1 Tellyfish. The upper three are medusae, members of the phylum Coel- 

 enterau The lower two are comb jellies, in the phylum Ctenophora. (Medusae redrawn 

 from Mayer; Mnemiopsis from Hyman; Hormiphora from Chun.) 



Long Island Sound and G. vertens is found in Puget Sound. Like most 

 medusae it does not merely float in the water, but moves rhythmically 

 up and down through a span of several feet. The upward movement is 

 active, produced by repeated, slow, graceful contractions of the body. 

 The contracting muscle fibers are arranged circularly just beneath the 

 epidermis of the lower or subumbrellar surface of the umbrella, and 

 also in the velum, a delicate membrane extending inward from the 

 lower edge of the umbrella. Contraction closes the umbrella, contraction 

 of the velum reduces the size of the opening beneath the umbrella, and 

 the downward jet of water produced pushes the animal upward. Be- 

 tween contractions elasticity of the body reopens the umbrella. Through- 

 out the pulsing ascent the sixty to eighty tentacles on the umbrellar rim 



