ached buds or reproductive bulbs, which become separate
individuals, and only after these and several successive generations
of individuals have been thus produced "asexually," by fission or by
budding, does a generation appear which produces true egg-cells and
sperm-cells and reproduces by their means. Thus it is true that the
individuals "budded off" or separated by fission from an asexual
parent can be ultimately traced through one or more generations of
previous asexual parents to an egg-cell produced and fertilised in the
regular way, and with this important modification Harvey's dictum is
justified. These facts and the wonderful histories of the animals and
plants in which egg-and-sperm-producing generations "alternate" with
generations which multiply by fission and budding have only been
worked out in detail and by the aid of the microscope during the great
century of scientific discovery which lies just behind us. Often the
two generations, reproducing, the one by fission, the other by egg and
sperm-cells, are alike in appearance, but often they are very
different, and have naturally been supposed at first to have nothing
to do with each other.

Thus some of the little "coralline polyps" and other most beautiful
little marine flower-like polyps attached to rocks, weeds, and shells
in the sea reproduce by budding and division. But after a period of
such growth and such budding they produce on their stalks--jelly-fish!
These jelly-fish are budded and thrown off by them, as glass-like
swimming bells, which lead an independent life, seize prey, nourish
themselves, and grow to a size varying from that of a sixpence to that
of a cart-wheel. These "bells" are commonly known as "jelly-fish."
They discharge thousands of egg-cells into the sea and fertilise them
with sperms! From those fertilised eggs grow young polyps, which fix
themselves to rocks or weeds, and grow up to bud and multiply by
fission, and eventually to produce again by fission a generation of
jelly-fishes! Such a marvellous history of alternating modes of
reproduction has been discovered, and described in greatest
microscopic detail and with most ample pictorial representations of
all the minutest structures of the organisms studied, not only in many
marine polyps, but also in the case of many parasitic worms, such as
the tape worms and the liver-flukes. Some of the most fascinating
cases, on account of the beauty of the little creatures concerned, are