These move away from each other, and become centres of attraction for
the enveloping matter, the protoplasm. The same direct cleavage of the
nuclei is also witnessed in the reproduction of many other protists,
while other unicellular organisms show the indirect division of the
cell.

Hence, although the amoeba is nothing but a simple cell, it is
evidently able to accomplish all the functions of the multicellular
organism. It moves, feels, nourishes itself, and reproduces. Some
kinds of these amoebae can be seen with the naked eye, but most of
them are microscopically small. It is for the following reasons that
we regard the amoebae as the unicellular organisms which have special
phylogenetic (or evolutionary) relations to the ovum. In many of the
lower animals the ovum retains its original naked form until
fertilisation, develops no membranes, and is then often
indistinguishable from the ordinary amoeba. Like the amoebae, these
naked ova may thrust out processes, and move about as travelling
cells. In the sponges these mobile ova move about freely in the
maternal body like independent amoebae (Figure 1.17). They had been
observed by earlier scientists, but described as foreign
bodies--namely, parasitic amoebae, living parasitically on the body of
the sponge. Later, however, it was discovered that they were not
parasites, but the ova of the sponge. We also find this remarkable
phenomenon among other animals, such as the graceful, bell-shaped
zoophytes, which we call polyps and medusae. Their ova remain naked
cells, which thrust out amoeboid projections, nourish themselves, and
move about. When they have been fertilised, the multicellular organism
is formed from them by repeated segmentation.

It is, therefore, no audacious hypothesis, but a perfectly sound