a. =Lower Organisms.=--As an example of a lower organism we may take the _amoeba_. If one watches an amoeba under the microscope he may see it move about the field, creeping along the surface of the glass plate; throwing out a pseudopodium here; invaginating a mouth or stomach there; taking in and digesting minute plant organisms; transporting itself across the field of the microscope through the aid of improvised locomotory organs. All these activities are egoistic. The amoeba is putting forth effort to gain its sustenance; it is sacrificing energy to receive compensation in the form of support. If we continue to watch this minute organism we will find that sooner or later it goes into a resting stage which does not last long before we can observe important internal changes making themselves manifest first at the nucleus, which slowly divides into two equal portions that separate, each carrying with it about half of the protoplasm of the parent organism. As these two young amoebae lie side by side under the microscope the thoughtful student will inquire--what has become of the parent organism? Whereas at first there was one mature amoeba, now we have before us two young amoebae of the next succeeding generation. The parent organism has sacrificed its substance and its individuality absolutely and completely for the next generation. [Illustration: Plate I Reproduction in the Amoeba.] It may be said in general that _reproduction always involves a division of the parent organism_. In the case of the amoeba the division is into two equal portions. In the case of some of the lower plants and animals the substance of the parent organism is divided into many equal minute spores or eggs, each of which develops a new organism. b. =Higher Organisms.=--These also suffer a division of their body protoplasm. However, instead of dividing into two or more equal parts and merging their individuality immediately into the next generation, the higher organisms divide off a very small portion of their protoplasm to make an egg or seed while the parent organism lives on to produce eggs or seeds on subsequent occasions. While the parental sacrifice in eggs or spermatozoa is minute and inconsiderable in the higher animals, the sacrifices subsequent to this initial division are incalculably greater in higher animals than in the lower organisms. We can cite no better example than the human subject. The human ovum, divided off from the maternal organism, is a minute globule of protoplasm, almost microscopic in size. The sacrifice of the mother in producing the ovum is inconsiderable, but the production of the ovum is simply the first step in the sacrifice which the maternal organism makes.