28 
THE ORGANIC CELL 
Weismann’s Theory of Reduction. 
The object of the process of reduction of the chromosomes 
in the germ- cells is to maintain the constant number character- 
istic of the species, for without such a reduction the number 
A, B. Division of one of the spermatogonia showing the full number 
(four) of chromosomes. C. Primary spermatocyte preparing for division ; the 
chromatin forms two tetrads. D, E, F. First division to form tv/o secondary 
spermatocytes, each of which receives two dyads. G, H. Division of the two 
secondary spermatocytes to form four spermatids. Each spermatid receives 
two single chromosomes and a centrosome which passes into the middle-piece 
of the spermatozoon. 
would be doubled in each succeeding generation. Why should 
the number of chromosomes for a species be constant ? Weis- 
mann’s theory is based on a paper written by W. Roux in 
