HYDRA. 25 



The Hydra,* the history of which is so curious and important 

 as to demand our special notice. This little creature resembles 

 a small portion of green transparent thread, fastened by one end 

 to the stems of water-plants, while the other is furnished with 

 several radiating filaments of extreme tenuity, which float freely 

 in all directions : should one of the numerous water-fleas, or any 

 other minute animal, come in contact with these floating filaments, 

 though it touch but the tip of one of them, it is at once arrested 

 in its course, and in spite of all its struggles dragged to the central 

 mouth, which opens to receive the helpless prey. 



The body of the hydra consists simply of a little gelatinous 

 bag, the margins of which are furnished with filaments employed 

 as tentacles, whilst at the opposite end there is a little sucker 

 whereby it fixes itself to foreign objects. The microscope reveals 



FIG. 17. LONG-ARMED HYDRA. 



the substance of these creatures to be composed entirely of a 

 transparent glairy matter, in which granules of slightly greater 

 opacity may be observed to float. Notwithstanding this sim- 

 plicity of structure, however, they are able to move from place to 

 place by fixing alternately the extremities of their body after the 

 manner of a leech, and they are sensible to the presence of light, 

 which they always approach. 



But their most wonderful attribute is that of being able inde- 

 finitely to reproduce any part of their body which may be cut off. 

 If a hydra be cut into pieces, each individual fragment, however 

 small, will speedily become a perfect animal, in all respects like 

 the original, the parts which were defective being produced in 

 their proper situation. If with fine scissors we slit one half-way 

 down, the result will be a hydra with two mouths, each surrounded 



* Hydra, a fabled monster that reproduced its heads as fast as they were cut off. 



