CORAL-MAKERS AND JELLY-FISH 97 



full-sized Aurelia. I have only once had the chance of 

 witnessing this beautiful sight, and that was many years 

 ago in a tank at the Zoological Gardens (they have no 

 such tanks now), where the polyp-like young (called 

 i *' Hydra tuba ") spontaneously put in an appearance, and 

 proceeded to break up into piles of little disks, which 

 separated and swam off as one watched them. The 

 French poet, Catulle Mend^s, imagined a world where 

 the flowers flew about freely and the butterflies were 

 fixed to stalks. His fancy is to some degree realized 

 by the swimming away of the young jelly-fish from their 

 stalks. There are a host of very minute jelly-fish, 

 measuring when full grown only half an inch or less in 

 diameter. They originate as buds from small branching 

 polyps, one kind of which is common on oyster-shells, 

 and is called " the herring-bone coralline." The dried 

 skins of these coralline polyps (which are horny) are 

 often to be picked up with masses of seaweed on the 

 seashore after a storm. The little jelly-fish are the ripe 

 individuals of the polyps, and produce eggs and sperm 

 which grow to be polyp-trees. These, again, after 

 growing and branching as polyps, give rise to little 

 jelly-fish here and there on the tree, which in most 

 kinds (though not in all) break off and swim away 

 freely. 



