82 
THE ORGANIC CELL 
poles, the egg dividing transversely into two cells (F). This 
phenomenon of division is repeated continuously, and from 
the resulting mass of cells is developed the new organism. 
The centrosome, which must be regarded as the dynamic 
centre, the presence of which initiated these various changes, 
is derived solely from the spermatozoon, the egg on the other 
hand supplying the yolk and the bulk of the cytoplasm. 
Individuality of the Chromosomes. 
It is an established fact that a nucleus is never formed de 
novo, but must arise by the division of a pre-existing nucleus. 
In mitosis the chromatin is resolved into bodies called chromo- 
somes, which have the power of growth and division, the same 
as the nucleus, forming in fact morphological individuals 
of a lower grade than the nucleus. This individual inde- 
pendence of the isolated chromosome has been strongly main- 
tained by Rabl and Boveri. Rabl concluded that ‘ the chromo- 
somes do not lose their individuality at the close of division, 
but persist in the chromatin reticulum of the resting nucleus. 
The so-called loss of identity during the resting stage is only 
apparent. At the commencement of the next division they 
again appear, the chromatic substance flowing back, through 
predetermined paths, into the primary chromosome-bodies/ 
From many observations made, it would appear that, 
whatever be the number of chromosomes entering into the 
formation of a reticular nucleus, the same number always 
issues from it — this result proving that the number of chromo- 
somes is due to the morphological organisation of the nucleus. 
Boveri confirmed this in echinoderms, by removing the nuclei 
from egg-fragments and fertilising these enucleated portions 
with single spermatozoa, the result being that the nuclei of such 
larvae contain only half the normal number of chromosomes. 
As further evidence, Van Beneden and Boveri showed clearly 
in Ascaris that during the development of the spireme the 
chromosomes actually appear in the same position as those 
which formed the reticulum. During the divergence of the 
chromosomes, the free ends are directed towards the mesial 
plane, and on the reconstruction of the daughter -nuclei these 
