CLASS SCYPHOZOA 



THE LARGE JELLYFISHES 



THERE is perhaps no marine animal which excites more wonder 

 than the jellyfish. Its transparency, its graceful rhythmical 

 movements, its long streaming tentacles, the variety and eccen- 

 tricity of its form, and often of its color, attract attention, and 

 one naturally desires to know something of its life-history. Jelly- 

 fishes are also called medusce, because their long appendages sug- 

 gest the locks of the Gorgon ; acalephs, on account of their stinging 

 or nettle-like properties ; and sun-jellies, sea-blubbers, etc., be- 

 cause they float upon the surface during the warmest part of the 

 day, when the sun is high. The name jellyfish is inappropriate, 

 since the animal in no way resembles a fish except in the fact 

 that it swims ; but it is, nevertheless, the commonest name. 



Jellyfishes vary in size from that of a piuhead to six or seven 

 feet in diameter. They differ in the number, size, and position 

 of the tentacles, the number of the radial canals, the form of the 

 manubrium, the position of the egg-sacs, etc. ; but the general 

 plan of the internal structure is the same in all species. In shape 

 they are compared to a mushroom. From the center of an um- 

 brella-like top falls a central organ like the stalk of a mushroom. 

 It is called the manubrium and is the mouth and stomach of the 

 animal. 



From the top of the manubrium radiate straight or branched 

 tubes, which are connected with a canal which runs around the 

 whole margin of the umbrella. Extending around the inner 

 circumference of the disk in certain species (usually the hydroid 

 medusas), there is a horizontal shelf, called the velum, or veil, be- 

 cause it sometimes falls like a veil. 



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