he protoplasm is due (Fig. 23, _b_). In this liquid
no structure can be determined, and, so far as we know, it is
homogeneous. Still further study discloses other complexities. It
appears that the fibrous material is always marked by the presence of
excessively minute bodies, which have been called by various names, but
which we will speak of as _microsomes_. Sometimes, indeed, the fibres
themselves appear almost like strings of beads, so that they have been
described as made up of rows of minute elements. It is immaterial for
our purpose, however, whether the fibres are to be regarded as made up
of microsomes or not. This much is sure, that these microsomes
--granules of excessive minuteness--occur in protoplasm and are closely
connected with the fibres (Fig. 23, _a_).

==The Nucleus.==--(a) _Presence of a Nucleus_.--If protoplasm has thus
become a new substance in our minds as the result of the discoveries of
the last twenty years, far more marvelous have been the discoveries
made in connection with that body which has been called the nucleus.
Even by the early microscopists the nucleus was recognized, and during
the first few years of the cell doctrine it was frequently looked upon
as the most active part of the cell and as especially connected with its
reproduction. The doctrine of protoplasm, however, so captivated the
minds of biologists that for quite a number of years the nucleus was
ignored, at least in all discussions connected with the nature of life.
It was a body in the cell whose presence was unexplained and which did
not fall into accord with the general view of protoplasm as the physical
basis of life. For a while, therefore, biologists gave little attention
to it, and were accustomed to speak of it simply as a bit of protoplasm
a little more dense than the rest. The cell was a bit of protoplasm with
a small piece of more dense protoplasm in its centre appearing a little
different from the rest and perhaps the most active part of the cell.

As a result of this excessive belief in the efficiency of protoplasm the
question of the presence of a nucleus in the cell was for a while looked
upon as one of comparatively little importance. Many cells were found to
have nucleii while others did not show their presence, and microscopists
therefore believed that the presence of a nucleus was not necessary to
constitute a cell. A German naturalist recognized among lower animals
one group whose distinctive characteris