the picture, but p h is the throat, and this is followed by the sac-like "stomach-intestine" d. These worms propagate likewise by simple fission, after a new brain-ganglion has been formed at th s t, by the thickening of the two sides. A new mouth is formed by a drawing in of the outer skin. On either side of the head there is a little indentation in which longer hairs are growing. These are probably organs of sense; however, their function has not yet been determined.
Figs. 7 and 8 show a pair of crab-like animals, which are among the regular inhabitants of wells. Fig. 7 is a cyclops; Fig. 8 represents a crustacean, the Cypris. The latter is rather a peculiar object, as the animal is inclosed in a shell-like structure, called a carapace, from which only a pair of caudal appendages 
Fig. 8 protrude, which are provided with bristles and serve for the purpose of locomotion; oc is the eye.
A considerable number of species of cyclops are to be found in the mud of wells. Fig. 7 shows the Cyclops nanus. This little animal travels rapidly through the water by means of its swimming apparatus, to which the powerful muscles (m) lend considerable assistance. The female carries two ovisacs (ei) with numerous eggs; oc, at the front part of the body, is the eye, which is of a reddish or brown color and possesses a fine lens.
In this article we have enumerated and pictured only the principal representatives of this fauna of the wells, so that a general idea might be gained of the appearance of the animals which live in the turbid water of wells. However, to show how rich in numbers this little animal world is, the fact should be mentioned that Prof. Vejdovsky, after his careful examination of the water of two hundred and thirty-one wells of Prague, was able to announce the existence of—(1) twenty varieties of amœba-like organisms; (2) twelve varieties of flagellate infusoria; (3) forty-five varieties of other infusoria; (4) twenty-four varieties of worms; (5) ten varieties of Crustacea—making altogether a total of one hundred and eleven species of organisms. Most of these varieties were found in wells which had been polluted by the infiltration of urine and decaying organic matter. The organisms carried down by the surface water into these lower regions had found abundant food there, and were thus enabled to continue their existence. With regard to the question as to whether the water from wells that show an abundance of these forms of life is dangerous
