THE WEST AMEBICAN SCIENTIST. 73 



and similar objects, while its slender, tendril-like tentacles are 

 slowly and gracefully waving about in search of prey. The body 

 and tentacles, when fully extended, seldom measure over one- 

 fourth or one-half of an inch in length, except in the case of the 

 rare species H. fusca, which sometimes attains a length of several 

 inches, owing to the extraordinary development of the tentacles, 

 which in that species are many times the length of the body. 

 The tentatles of Hydra are hollow, each being traversed by a 

 canal communicating directly with the body cavity. The body 

 and tentacles are possessed of most remarkable extensile and con- 

 tractile powers. At one moment the animal may be extended to 

 such a degree that the tentacles are almost invisible by reason of 

 their fineness, when upon being disturbed it immediately con- 

 tracts until it appears like a minute, jelly-like lump, studded with 

 a few stubby knobs. It then slowly expands until it is again 

 fully extended. The little creature is extremely voracious. It 

 subsists entirely on animal food, consisting mainly of minute 

 worms and the smaller entomostraca. When the prey has been 

 caught by means of the tentacles, these contract, and the unfor- 

 tunate victim is forced with remarkable violence into the diges- 

 tive cavity of the polype, the softer parts being there absorbed 

 and the undigested portions ejected through the mouth. Of all 

 the many marvelous properties possessed by this remarkable little 

 organism, perhaps the most extraordinary is its power of repro- 

 ducing lost parts. If the body be cut into numerous pieces, each 

 developes into a perfect animal. If the tentacles be severed from 

 the body, they soon obtain a new body, and the body from which 

 they were cut produces a new set of tentacles. Innumerable ex- 

 periments have been made, showing the almost incredible vitality 

 of every part of this little animal. Some remarkable instances of 

 abnormal development in Hydra were alluded to and a descrip- 

 tion given of two curious parasitic infusoria by which it was often 

 infested. After referring to the wide geographical distribution 

 of the animal and describing the species found in California, Mr. 

 Breckenfeld concluded as follows: 'The little plant-animal, which 

 we have been considering to-night, has been a celebrity in the 

 scientific world for nearly a century and a half. Nor is this to be 

 wondered at, for in the whole range of microscopic life there are 

 few if any animals possessing equally attractive features to the in- 

 vestigator. Its graceful movements and interesting food habits, 

 its comparatively simple structure, its plant-like appearance, its 

 wonderful methods of reproduction and the important light which 

 many facts in its histology have thrown upon the elucidati($n of 

 structure in the higher animals — all invite attention and study. 



