THE ORGANIC CELL 
29 
1883. Roux argued that in order to understand and account 
for the complex process of mitosis it must be assumed that 
the chromatin differs in different regions, representing certain 
qualities in some, and others in other portions. He insisted 
that, if the chromatin was the same throughout, the process 
of direct division would be quite as effective as the very com- 
plicated process of karyokinesis, and this intricate method, 
by which there is an exact longitudinal splitting of the thread, 
would be a mere waste of energy. 
Weismann’s explanation of the process of fertilisation is 
that it brings about new mixtures of different ‘ ids.’ The 
term 4 id ’ used by him represents the visible chromatin granules, 
which are arranged in a linear series to form 4 idants ’ or 
chromosomes. 
The number of 4 ids,’ however, would be doubled by the 
union of two germ-nuclei ; and should there not be a reduction 
of the chromatin prior to this union, in a few generations it 
would become exceedingly complicated. From his assumption 
that the ancestral germ-plasms (ids) are arranged in a linear 
series in the spireme thread, or the chromosomes derived from 
it, he prophesied that two kinds of mitosis would occur : the 
first a longitudinal division of the thread, which would bring 
about an equal distribution of the ancestral plasms to the 
daughter nuclei ; the second form of division which he postu- 
lated was of such a character that each daughter-nucleus 
would receive half the number possessed by the mother- nucleus. 
He also assumed that this was brought about either by a 
transverse division of the chromosomes or by getting rid of 
complete chromosomes without division. Weismann, pursuing 
the subject still further, maintained that the reduction 
must be involved in the formation of the polar bodies, and 
in the similar phenomena occurring during spermatogenesis. 
Weismann’s prophecy has been verified by the most rigid 
microscopical scrutiny. As Boveri has said : 4 Thus, at some 
stage or other in the generation series of the germ-cells, there 
occurs a reduction of the number of chromosomes originally 
present to one half, and this numerical reduction is therefore 
to be regarded, not as a mere theoretical postulate, but as a 
fact.’ 
