A freshwater Hydra, growing on the duckweed usually multiplies by budding. It forms daughter-buds, living images of itself; a check comes to nutrition and these daughter-buds go free. A big sea-anemone may divide in two or more parts, which become separate animals. This is asexual reproduction, which means that the multiplication takes place by dividing into two or many portions, and not by liberating egg-cells and sperm-cells. Among animals as among plants, asexual reproduction is very common. But it has great disadvantages, for it is apt to be physiologically expensive, and it is beset with difficulties when the body shows great division of labour, and is very intimately bound into unity. Thus, no one can think of a bee or a bird multiplying by division or by budding. Moreover, if the body of the parent has suffered from injury or deterioration, the result of this is bound to be handed on to the next generation if asexual reproduction is the only method. [Illustration: _Photos: J. J. Ward, F.E.S._ A PLANT-LIKE ANIMAL, OR ZOOPHYTE, CALLED OBELIA Consisting of a colony of small polyps, whose stinging tentacles are well shown greatly enlarged in the lower photograph.] [Illustration: _Reproduced by permission of "The Quart. Journ. Mic. Sci."_ TRYPANOSOMA GAMBIENSE (Very highly magnified.) The microscopic animal Trypanosome, which causes Sleeping Sickness. The study of these organisms has of late years acquired an immense importance on account of the widespread and dangerous maladies to which some of them give rise. It lives in the blood of man, who is infected by the bite of a Tse-tse fly which carries the parasite from some other host.] [Illustration: VOLVOX The Volvox is found in some canals and the like. It is one of the first animals to suggest the beginning of a body. It is a colony of a thousand or even ten thousand cells, but they are all cells of one kind. In _multicellular_ animals the cells are of _different_ kinds with different functions. Each of the ordinary cells (marked 5) has two lashes or flagella. Daughter colonies inside the Parent colony are being formed at 3, 4, and 2. The development of germ-cells is shown at 1.] [Illustration: PROTEROSPONGIA One of the simplest multicellular animals, illustrating the beginning of a body. There is a setting apart of egg-cells and sperm-cells, distinct from body-cells; the collared lashed cells on the margin are different in kind from those farther in. Thus, as in indubitable multicellular animals, division of labour has begun.]