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._