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POPULAR SCIENCE MONTHLY. 



wanted, to take it out, either with the pipette or the forceps, and 



transfer it to the trough. By holding it up to the light one can 



readily see whether it is worth while to sit down at the other 



I <2 table and use the much more 



powerful aid of the binocular 

 microscope. 



My friends, it is true, laugh 

 at me, and I laugh at them. They 

 wonder why I am so devoted to 

 " a glass globe full of water, with 

 a few plants and snails," and I 

 tell them that while they see 

 much to admire in horticulture, 

 agriculture, and a host of other 

 "cultures," I am an enthusiast 

 about hydra-culture. Indeed, in 

 this small and insignificant aqua- 

 rium I have a flock of fresh- 

 water polyps, called "hydras," 



Fig. 2. The Fresh-watee IItdra hanging 



FROM DUCKWEEP IN A i'OND : 1, tlie loUff- 



armed hydra i Hijdra fi/sca) feeding ; a a, 

 small animals caught in it arms ; 2, short- 

 armed hydra (IJi/Jra viridis) throwing 

 off yoxing hydi-a buds, b b. 



full of interest, full of wonder. I envy Trembley, who in 1744 

 published A Memoir on the Fresh- water Polyp, the intense pleas- 

 ure he felt in unraveling the life history of these creatures. He 

 was investigating the unknown when he studied the strange phe- 

 nomena connected with them, and was transported with astonish- 

 ment. I know, from the labors of others, what to expect, and yet 

 I am lost in wonder. 



We may be thankful that these animals are as small as they 

 are ; for, if they were only a few feet in length, we should have 

 in our water world many a repetition of the devastation said to 

 have been caused by the Lernsean Hydra, whose destruction was 

 one of the gigantic labors of the hero Hercules. As it. is, the 

 longest you can find is only an inch in length. They can, how- 

 ever, be easily seen with the unaided eye, and with the help of a 

 pocket lens can to some extent be studied. In fact, Trembley, 

 the famous observer of them, had nothing better. It is only 

 when we wish to examine minute details that the use of the 

 elaborate microscope is called for. A group of them attached to 

 the rootlets of duckweed or the under side of the leaves or on 

 the stems of plants is a curious sight. A nearer view may often 

 be obtained, for they will attach themselves to the side of the 

 glass to enjoy the light, which they seem to love. 



The commonest species of hydras may easily be distinguished 

 by their color, one being usually a reddish brown, while the 

 other is a vivid green. The particular shade of color of the 

 former depends on the nature of the food captured ; and it is said 

 that it has been colored blue, red, and white by feeding it with 



