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INTRODUCTION TO CYTOLOGY 



1908), Meves (1907, 1908, 1911), Giglio-Tos (1908), and Granata (1910), 

 reject the theor}- of chromosome individuality and specificity, and 

 therefore do not regard the chromosomes which are distributed to the 

 four cells at maturation as at all identical with those of the divisions im- 

 mediately preceding, except in so far as they are composed of the same 

 nuclear material. Accordingly they recognize no qualitative reduction, 

 but only a numerical one. This reduction in number results from the 

 fact that the spireme formed in the heterotypic prophase (Fig. 99, A) 

 segments into the haploid number of pieces instead of the diploid number, 

 these pieces being simply divided longitudinally at both maturation 

 divisions, and the four resulting nuclei being qualitatively similar. 



.i 



fin (0) (? 





B 



C 



kA © 



Fig. 99. — Diagram showing three reported modes of numerical reduction with- 

 out qualitative reduction. 

 A, according to Fick et al. B, according to Vejdowsky; complete fusion of conjugating 

 members. C, according to Bonnevie; bivalents arranged on spindles in juxtaposition; 

 fusion of conjugating members eventually becomes complete. 



According to Vejdowsky (1907) (Fig. 99, B) the chromosomes appear 

 in diploid number in the heterotypic prophase and conjugate parasynapti- 

 cally. The members of the pair fuse completely and lose their individual 

 identity, so that the chromosomes appearing on the first maturation 

 spindle in haploid number are new entities, and not merely temporary 

 pairs of somatic chromosome individuals. At both divisions these bodies 

 split longitudinally, giving equivalence to the four resulting nuclei. 

 Here, as in the foregoing example, there is no definite qualitative reduc- 

 tion in Weismann's sense, though a numerical reduction is brought about 

 by means of a complete fusion at the time of chromosome conjugation. 



