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 







H 



K 



Fig. 120. Reduction in the spermatogenesis ofAscarts megalocephala^xt. bivalens. [BRAUER.] 1 

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

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

 thread, B. This shortens (C), and breaks in two to form the two tetrads (D in profile, E viewed 

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

 /. Secondary spermatocyte. y. 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 i883, 2 in which are 



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

 univalens see Fig. 148. 



2 Uber die Bedeutung der Kerntheilungsjiguren. 



