Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] PROTOZOA 183 The amoeba, like other one-celled organisms, reproduces by the process of fission. A single cell divides by splitting into two others, each of which resembles the parent cell except that they are of less bulk. When these become the size of the parent amoeba, they in turn each divide. This is a kind of asexual repro- duction. When conditions unfavorable for life come, the amoeba, like some one-celled plants, encysts itse
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] PROTOZOA 183 The amoeba, like other one-celled organisms, reproduces by the process of fission. A single cell divides by splitting into two others, each of which resembles the parent cell except that they are of less bulk. When these become the size of the parent amoeba, they in turn each divide. This is a kind of asexual repro- duction. When conditions unfavorable for life come, the amoeba, like some one-celled plants, encysts itself within a membranous wall. In this condition it may become dried and be blown through the air. Upon return to a favorable environment it begins life again as before. From the study of the amoebahke organisms which are known to cause malaria and by comparison with the amcebae which Hve in our ponds and swamps, it seems Hkely that every amoeba has a compHcated hfe history during which it passes through a sexual stage of existence. Such a stage is seen in the conjugation of the paramoecium. The Cell as a Unit. — In the daily life of a one-celled animal we find the single cell performing all the activities which we shall later find the many-celled animal is able to perform. In the amoeba no definite parts of the cell appear to be set off to perform certain func- tions; .but any part of the cell can take in food, can abs-orb oxygen, can change the food into protoplasm and excrete the waste material. The single cell is, in fact, an organism. One-celled Plants and Animals Compared. — In our consideration of the alg2e we found that the sim- plest of all plants consists of a single cell. This cell might be fixed in one place, as the common form of pleurococcus, or it might move about by means of cilia (as seen in the motile stage of pleurococcus and in many other single cells considered to be plants). While single-celled animals are usually free-swimming, nevertheless some (especi
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