564 REPORT—1905. 
All these are permanent organs of the cell, produced in the first instance as a result 
of the cell activity, but now capable of an independent existence in the cell, in 
that they reproduce themselves by division, and are in this way carried on 
from cell to cell. 
In many cells there are formed at certain stages other organs which appear to 
be transitory, and are only produced when they are required. Such are the spindle 
figure, the centrosome, the blepharoplast, and the ccenocentrum. 
So far as we know, the cell is the smallest vital unit that can have a separate 
existence. But it is only among the unicellular organisms and under certain con- 
ditions in the earlier stages of development of the more highly organised multi- 
cellular otganisms that cells have a perfectly independent life. Schwann’s 
hypothesis that the multicellular body is a colony of independent vital activities 
governing the nutrition, growth, and reproduction of the whole is not tenable. 
The cell cannot be regarded as an independent unity working merely in asso- 
ciation with other cells. Its life and existence depend upon these. It is an integral 
part of an individual organisation, and cannot exist apart from it. But this 
absolute dependence of individual cells upon the organisation as a whole is only 
realised in the more highly developed forms. In the lower types of plants (and 
animals) it is possible, during the early stages of development, to separate a single 
cell from the whole, which will still continue to live and grow. ach cell is no 
doubt dependent upon the others to some extent, even at this early stage, but it 
still retains the power to develop independently if placed under suitable conditions, 
As cell division continues each cell becomes more and more dependent upon its 
fellows, until the stage is reached when it no longer has the power to exist by itself. 
The various functions performed by a cell reside within it as an individual unit, 
but the exercise of these functions is governed by the organism asa whole. Just 
as the organism seeks for a state of equilibrium in relation to various external 
stimuli, so a cell in an organism has to adapt itself to and come into a state of 
equilibrium with the various cells around it. 
The Nucleus. 
The nucleus is the centre of activity, and governs the vital functions of the cell. 
All investigations show that in its absence the cell soon ceases to perform its vital 
functions and dies. 
In all cells, from the algze and fungi upwards, the nucleus is more or less clearly 
delimited from the cytoplasm by a membrane or limiting layer. The important 
substance which is thus separated off from the rest of the cell is the chromatin, 
probably the most complex and most highly differentiated chemical compound or 
collection of compounds in the cell. It exists in the form of a more or less 
granular network, and is characterised chemically by the presence of phosphorus, 
which is in organic connection with it. We may look upon the chromatin as the 
highest point in the development of living substance, upon which the activities of 
the cell in great measure depend, and as the seat of origin of all those complicated 
changes which have for their ultimate aim the division of the cell. 
The division of the nucleus begins by a series of transformations in the 
chromatiu network which lead to the differentiation in it of chromosomes. We 
know very little of what actually takes place during these changes, and practically 
nothing of the forces at work to bring them about. But the visible result is that 
the chromatin granules gradually fuse together, or become restricted to certain 
areas by the increased vacuolation of the ground substance of the nucleus to 
form a thick, more or less regular thread, in which can be observed at certain 
stages a differentiation into alternate regions of stainable and unstainable sub- 
stance—chromatin and achromatin—which finally breaks up into equal or un- 
equal lengths to form the chromosomes. In some cases the chromatin granules or 
network become aggregated into a definite number of irregular masses which 
form oa chromosomes directly without the production of a distinct chromatin 
thread. 
This nuclear differentiation is usually accompanied by changes in the 
