They are found abundantly in ponds and ditches, and in salt water. Sometimes they are so abundant in drinking water that has not been filtered, as to alarm a timid person, but you will find them just as good to eat raw as they are cooked. The most common of these little creatures is the _Cyclops Quadricornis_, so called because he has one eye and four horns. (_Fig. 2._) This picture represents a female, and she carries her eggs in the two little black bags that you see fastened on each side of the abdomen. You will find it very interesting by and by to watch the eggs hatch and see the little cyclops hop away. When young they do not look much like their parents; they are rounder and their legs are more prominent. The female cyclops (the male is comparatively rare) is the most common creature in Cochituate water, and as it is constantly eating, it helps to purify the water, and, in its turn, is eaten by the fishes. In swimming it contracts its four horns and its fringed feet with a quick movement that throws it forward through the water with a leap. Its one eye is of a brilliant red, and is a beautiful object under the microscope. The shell also is sometimes beautifully colored, and is often transparent, so that the internal organs are plainly visible through it. [Illustration: FIG. 5.] Another of the family of _Cyclopidae_ is the _Canthocamptus minutus_ (_fig. 3_), which you see is longer and more tapering in its form than the _Cyclops Quadricornis_. It is also very common and very active. _Chydorus Sphoericus_ (_fig. 4_) is a very pretty round form interesting to study when transparent. All these and some others with rather hard names are in that division of the _Crustacea_ called _Entomostraca_, meaning shelled creatures whose shells are cut and do not cover them all round. On this principle, an oyster on the half-shell might be called an _Entomostracan_. Now to catch these lively fellows, you must take a dipping tube and be patient, and when you have got one in the tube, carefully drop it on the bottom of the "live-box" (_fig. 5_), and put on the cover. Examine it first with the lowest power you have. By careful management of the cover you can catch it between the top and bottom without breaking the shell, and in this prison you can study it at leisure. V.--COCHITUATE WATER. You have read or been told that if you look at a drop of water through a microscope you will find it full of animalculae, and showmen will sometimes exhibit water containing _entomostraca_ hopping about, and will try to persuade you that all water looks in the same way. [Illustration: ROTIFER VULGARIS.]