Page:Popular Science Monthly Volume 51.djvu/534

520 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 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 aquarium I have a flock of freshwater polyps, called "hydras," full of interest, full of wonder. I envy Trembley, who in 1744 published A Memoir on the Fresh-water Polyp, the intense pleasure he felt in unraveling the life history of these creatures. He was investigating the unknown when he studied the strange phenomena connected with them, and was transported with astonishment. 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 Lernæan 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, however, 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