Note that _Amœba_ has no mouth or alimentary canal; no nostrils or lungs, no heart or blood-vessels, no muscles, no glands. It is an animal body not made up of distinct organs and diverse tissues. Its whole body is a simple minute speck of protoplasm, a single animal cell. But it takes in food, it moves, it excretes waste matter from the body, is sensitive to the touch of surrounding objects, and, as we may be able to see, it can reproduce itself, i.e., produce new _Amœbæ_. _Amœba_ is the simplest living animal. It is only rarely that we can find an _Amœba_ actually reproducing. The process, in its gross features, is very simple. First the _Amœba_ draws in all of its pseudopodia and remains dormant for a time. Next, certain changes take place in the nucleus, which divides into equal portions, one part withdrawing to one end of the protoplasmic body, the other to the opposite end. Soon the body protoplasm itself begins to divide into two parts, each part collecting about its own half of the nucleus. Finally the two halves pull entirely away from each other and form two new _Amœbæ_, each like the original, but only half as large. This is the simplest kind of reproduction found among animals. _Amœbæ_ continue to live and multiply as long as the conditions surrounding them are favorable. But when the pond dries up the _Amœbæ_ in it would be exterminated were it not for a careful provision of nature. When the pond begins to dry up each _Amœba_ contracts its pseudopodia and the protoplasm secretes a horny capsule about itself. It is now protected from dry weather and can be blown by the winds from place to place until the rains begin, when it expands, throws off the capsule and commences active life again in some new pond. =The Slipper Animalcule= (_Paramœcium_ sp.)--_Technical Note_.--_Paramœcia_ can be secured in most pond water where leaves or other vegetation are decaying. However, if specimens are not readily secured place some hay or finely cut dry clover in a glass dish, cover with water and leave in the sun for several days. In this mixture specimens will develop by thousands. Place a drop of water containing _Paramœcia_ on a slide with cover-glass over it. Using a low power, note the many small animals darting hither and thither in the field. Run a thin mixture of cherry gum in water under the cover-glass. In this mixture they can be kept more quiet and be better studied. How does _Paramœcium_ (fig. 6) differ from _Amœba_ in form and movement? Has the body an anterior and a posterior end? The delicate, short, thread-like processes, on the surface of the body, which beat about very rapidly in the water are called _cilia_, and they are simply fine prolongations of the body protoplasm. What is their function? Note a fine _cuticle_ covering the body. Note also many minute oval sacs lying side by side in the ectosarc. These are called _trichocysts_ and from each a fine thread can be thrust out.