THE BEARERS OF THE HERITAGE 291 
This separation is followed by a similar constriction and final division 
of the entire cell-body, which results in the production of two new 
cells. This form of cell-division is known as simple or direct division. 
Such a simple division, while found in higher animals, is less frequent 
and apparently much less significant than another type of division 
which involves profound changes and rearrangements of the nuclear 
contents. The latter is termed mitotic or indirect cell-division. Fig. 44 
illustrates some of the stages which are passed through in indirect 
cell-division. The centrosome which lies passively at the side of the 
nucleus in the typical cell (Fig. 44, @) awakens to activity, divides and 
the two components come to lie at the ends of a fibrous spindle. In 
Centrosome. 
True 
nucleolus 
Nucleus.) (plasmosome). 
Chromatin e=——-—- 
network, Vacuole. 
Metaplasm a 
(passive bodies). 
Fic. 43.—Diagram of a cell, showing various parts. (From Guyer.) 
‘ 4 
the meantime, the interior of the nucleus is undergoing a transforma- 
tion. The granules and patches of chromatin begin to flow together 
along the nuclear network and become more and more crowded 
until they take on the appearance of one or more long deeply- 
stained threads wound back and forth in a loose skein in the nucleus 
(Fig. 44, 6). If we examine this thread closely, in some forms it may 
be seen to consist of a series of deeply-stained chromatin granules 
packed closely together, intermingled with the substance of the 
original nuclear network. 
As the preparations for division go on the coil in the nucleus breaks 
up into a number of segments which are designated as chromosomes 
(Fig. 44, ¢). The nuclear membrane disappears. The chromosomes 
