i88 



REDUCTION OF THE CHROMOSOMES 



this really be so, there can be here no reducing division in Weis- 

 mann's sense. The reduction of chromatin, caused by the ensuing 

 cell-division, is therefore only a quantitative mass-reduction, as Hert- 

 wig and Brauer insist, not a qualitative sundering of different ele- 

 ments, as Weismann's postulate demands.^ The work of Strasburger 

 and Guignard, considered at p. 195, has given in principle the same 

 general result in the flowering plants, though the details of the pro- 

 cess are here considerably modified, and apparently no tetrads are 

 formed. 



A 



E 



F 



Fig. 93. — Origin of the tetrads by ring-formation in the spermatogenesis of the mole-cricket 

 Gryllotalpa. [voM RATH.] 



A. Primary spermatocyte, containing six double rods, each of which represents two chromo- 

 somes united end to end and longitudinally split except at the free ends. B. C. Opening out of 

 the double rods to form rings. D. Concentration of the rings. E. The rings broken up into 

 tetrads. F. First division-figure established. 



We now return to the second view, referred to at p. 186, which 

 accords with Weismann's hypothesis, and flatly contradicts the con- 

 clusions drawn from the study of Ascaris. This view is based mainly 

 on the study of arthropods, especially the Crustacea and insects, but 

 has been confirmed by the facts observed in some of the lower verte- 

 brata. In many of these forms the tetrads first appear in the form 

 of closed rings, each of which finally breaks into four parts. First 

 observed by Henking ('91) in the insect PyrrocJwris, they have since 

 been found in other insects by vom Rath and Wilcox, in various cope- 



1 In an earlier paper on Braiichipiis ('92) Brauer reached an essentially similar result, 

 which was, however, based on far less convincing evidence. 



