e is no final decision between these
opposing views. Professor Wilson of Columbia has suggested that both may
contain a measure of truth.

Again, it is a question whether the finer granules seen within the cell
are or are not typical structures, "capable of assimilation, growth,
and division, and hence to be regarded as elementary units of structure
standing between the cell and the ultimate molecules of living matter."
The more philosophical thinkers, like Spencer, Darwin, Haeckel,
Michael Foster, August Weismann, and many others, believe that such
"intermediate units must exist, whether or not the microscope reveals
them to view." Weismann, who has most fully elaborated a hypothetical
scheme of the relations of the intracellular units, identifies the
larger of these units not with the ordinary granules of the cell, but
with a remarkable structure called chromatin, which becomes aggregated
within the cell nucleus at the time of cellular division--a structure
which divides into definite parts and goes through some most suggestive
manoeuvres in the process of cell multiplication. All these are puzzling
structures; and there is another minute body within the cell, called the
centro-some, that is quite as much so. This structure, discovered by
Van Beneden, has been regarded as essential to cell division, yet some
recent botanical studies seem to show that sometimes it is altogether
wanting in a dividing cell.

In a word, the architecture of the cell has been shown by modern
researches to be wonderfully complicated, but the accumulating
researches are just at a point where much is obscure about many of
the observed phenomena. The immediate future seems full of promise
of advances upon present understanding of cell processes. But for the
moment it remains for us, as for preceding generations, about the most
incomprehensible, scientifically speaking, of observed phenomena, that a
single microscopic egg cell should contain within its substance all the
potentialities of a highly differentiated adult being. The fact that
it does contain such potentialities is the most familiar of every-day
biological observations, but not even a proximal explanation of the fact
is as yet attainable.

THE ANCESTRY OF THE MAMMALS

Turning from the cell as an individual to the mature organism which
the cell composes when aggregated with its fellows, one finds the
usual complement of open questions, of greater or less significance,
focalizing