244 



REDUCTION OF THE CHROMOSOMES 



deeper meaning of the phenomena was first seriously considered by 

 Weismann in his essays of 1885 and 1887 ; and, although his conclu- 

 sions were of a highly speculative character, they nevertheless gave so 







'•Oo-OC"^ 



^y 





I 



Fig. 120. — Reduction in the spermatogenesis of Ascarts megalocephala,v9.x. bivalens. [Brauer.] 1 

 A- G. Successive stages in tVie division of tlie primary spermatocyte. The original reticulum 

 undergoes a very early division of the chromatin-granules which then form a doubly split spireme- 

 thread, 5. This shortens (C), and breaks in two to form the two tetrads (Z) in profile, £• viewed 

 endwise). F. G.H. First division to form two secondary spermatocytes, each receiving two dyads. 

 /. Secondary spermatocyte. J. K. The same dividing. L. Two resulting spermatids, each with 

 two single chromosomes and a centrosome. 



great a stimulus to the study of the entire problem that his views 

 deserve special attention. Weismann's interpretation was based on a 

 remarkable paper published by Wilhelm Roux in 1883,^ in which are 



1 For division of the spermatogonia see Fig. 55; for the corresponding phenomena in var. 

 univalens see Fig. 148. 



2 Vber die Bedeutung der Kerntheilungsjiguren. 



