The next earliest stage in the evolution of living matter, the nucleated cell, does exactly the same thing. The nucleus splits into two, each of which becomes a new nucleus for the protoplasmic matter of the original cell, and either multiply within it, or burst the old cell-wall and become two new cells resembling the first. The next stage in advance is that of propagation by germs or buds, in which the organism does not divide into two equal parts, but a small portion of it swells out at its surface, and finally parts company and starts on a separate existence which grows to the size of the parent by its inherent faculty of manufacturing fresh protoplasm from surrounding inorganic materials. This process may be witnessed any day in an aquarium containing specimens of the sea-anemone, where the minute new anemones may be seen in every form, both before and after they have parted from the parent body. It remains one of the principal modes of propagation of the vegetable world, where plants are multiplied from buds even after they have developed the higher mode of sexual propagation by seeds. In some of the lowest animals, such as worms, the buds are reduced to a small aggregation of cells, which form themselves into distinct individuals inside the body of the parent, and separate from it when they have attained a certain stage of development. Advancing still further on the road towards sexual reproduction, we find these germ-buds reduced to spores, or single cells, which are emitted from the parent, and afterwards multiply by division until they form a many-celled organism, which has the hereditary qualities of the original one. This is the general form of propagation of the lower plants, such as algæ, mosses, and ferns, and also of a number of the lower forms of animal-like microscopic organisms, such as bacteria, whose spores, floating in the air in enormous quantities, and multiplying when they find a fit soil with astonishing rapidity, in a few days devastate the potato crop of a whole district or bring about an epidemic of scarlet-fever or cholera. They have their use however in creation, and their action is beneficent as well as the reverse, for they are the principal cause of putrefaction, the process by which the dead organic matter, which, if not removed, would choke up the world, is resolved into the inorganic elements from which it sprang, and rendered available for fresh combinations.