108 
THE ORGANIC CELL 
cells from the somatic has been traced by Boveri back to the 
very first division of the egg. ‘ From the outset the progenitor 
of the germ-cells differs from the somatic-cells, not only in 
the greater size and richness of chromatin of its nuclei, but 
also in its mode of Mitosis ; for in all those blastomeres destined 
to produce somatic cells a portion of the chromatin is cast out 
into the cytoplasm, where it degenerates, and only in the germ 
cells is the sum total of the chromatin retained.’ 
The process is as follows : — Two long chromosomes are 
formed in each of the two cells resulting from the first division. 
These two cells divide, and a most striking result is at once 
noticeable. In the figure below at A such a two-celled, stage is 
seen from the poles, while at B the same two-celled stage is 
viewed from the side of the spindle. In the upper cell of A 
the division is normal, the two chromosomes splitting longi- 
tudinally, the halves passing to the extreme poles of the spindle, 
as seen in the upper cell in B. In the lower cell a very different 
phenomenon occurs — the central portions of the two chromo- 
somes are broken up into a lot of chromatin particles, which 
divide, and, as seen in the lower cell of B, these are the only 
portions of the chromosomes which are attracted to the poles 
of the spindle to form the nuclei after division. The massive 
outer ends of the chromosomes disappear in the cytoplasm 
and take no further part in forming nuclei. At C is seen the 
four-celled stage, and it will at once be noticed that the nuclei 
of the upper two cells are large and well defined, containing, 
as they do, the whole of the chromatin, while in the lower pair 
of cells the nuclei are pale and small, and lying external to 
them in the mesial plane are seen the masses of chromatin 
which have been cast off. At D the four-celled stage is seen 
with the mitotic figures of the next division. 
The upper two cells show the spindles from the sides, 
while the lower two give a view from the poles. In the upper 
left-hand cell the two complete chromosomes can be seen, each 
divided longitudinally, while in the upper right-hand cell we see 
a repetition of the phenomenon of reduction, the central portions 
of the chromosomes being broken up into granules preparatory 
to being drawn to the poles of the spindle to form the nuclei 
of the pair of somatic cells thus formed — the swollen outer 
