244 



REDUCTIOX OF THE CHROMOSOMES 



deeper meanin^^ of the phenomena was first seriously considered by 

 Weismann in his essays of 1S83 and 1887 ; and, although his conclu- 

 sions were of a highlv'speculative character, they nevertheless gave so 



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Fig. 120. — Reduction in the spermatogenesis of Ascaris mcgalocephala,v7iX. bivalens. [Brauer.] 1 



.^l-G. Successive stages in tlie division of the primary spermatocyte. The original reticulum 

 undergoes a ver)' early division of the chromatin-granules which then form a doubly split spireme- 

 tir'ad.Zf. This shortens (6), and breaks in two to form the two tetrads (Z) in profile, .fi" viewed 

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

 /. Secondary sp<Tmatocyte. J. K. The same dividing. Z. 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 whicTi arej! 



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

 univalens see Fig, 148. 



'^ Uber die Bedeiitiing der KerntheilungsfigHren. 



