122 CCELENTEKATA OR STINGING-ANIMALS. 



Stinging-animal, a degenerate representative — the Hydra, 

 which hangs from the stems and leaves of fresh-water 

 plants. It is so simple in structure that we may start afresh 

 with it, though in all likelihood it is rather at a terminus 

 than at the beginning of the series. 



This Hydra, which was first described in 1703 by 

 Leeuwenhoek, and studied by some of the old naturalists, 

 such as Rosel von Rosenhof and the Abb^ Trembley, 

 with natural eagerness, is in size very unlike the monster 

 with which Hercules contended, for it is only from one-sixth 

 to half an inch in length ; but it is like the mythical form in 

 its defiance of wounds. In fact, if we cut its tubular body 

 into fragments, each part may reproduce the whole. 



When the Hydra is feeding well, it buds oif daughter 

 forms, which remain for a while attached to the parent, 

 but are eventually set adrift and establish themselves inde- 

 pendently. A Hydra may be found with several daughter 

 buds, and these before leaving the parent may themselves 

 bear buds of yet another generation. 



If you suppose the budding of Hydra continued almost 

 indefinitely, you get an image of a "compound-Hydra," — a 

 hydroid colony, a zoophyte, such as you may find encrusting 

 the shore rocks and many marine objects. 



One of the most interesting and in some places com- 

 monest sights that you will see on the rocky shore is a 

 hermit-crab within its usual buckie shell, but covered by a 

 slightly pinkish crust of small polypes (^Hydractinia), which 

 may be found beautifully expanded in the still pool. They 

 are like Hydra in many ways, but they are members of a 

 budding colony, and are united at their bases by connecting 

 roots or canals. In such a crowded colony of many hun- 

 dreds, perfect liberty, fraternity, and equality are impossible ; 

 some are more favourably situated, and better fed, and con- 

 sequently more completely developed than others ; the fact 

 at least is that the colony of Hydractinia shows division of 

 labour among its members, some doing one thing, some 

 another. Most numerous are nutritive " persons " like the 

 Hydra, but besides these, and fed at their expense, are male 

 or female reproductive persons which produce sperms or 

 eggs, and eventually start new colonies. Again, however, 

 there are long, slender " persons," likewise mouthless, but 



