22 



CHROMOSOME THEORY OF HEREDITY 



among the results of the most eminent of observers that some writers gave expression to the 

 opinion that the problem was a barren one ; but within the last few years a new light has been 

 thrown on it by the work of numerous observers. The ultimate result has emerged in the 

 form of an interesting hypothesis which combines, in a fashion, the theories of Minot and 

 Weismann. 



In 1896 Moore described a phase in which the chromatin of the nucleus is clumped, which, 

 as already mentioned, he named the synapsis. This proved to be a very general phenomenon 

 in spermatogenesis, and although missed at first in oogenesis was shown by Winiwarter (1901) 

 to occur at an extremely early stage in the history of the oocyte. The idea that the double- 

 rod prophase heterotypical figures might arise from fusion of chromosomes was not quite a 

 new one. It had been suggested by Korschelt, Wilcox, and Calkins, but it took a new form 

 when by the observations of Winiwarter, Montgomery, Sutton, Farmer, and Moore, it was 



FIG. 31 (a to/). SOME STAGES IN THE MATUBATION OP THE EGG OF THE BABBIT, x 1700 diameters. 



(Winiwarter.) 



a, nuclear network converted into delicate looping threads; b, synaptic stage (fine threads); 

 c, synaptic stage (thick threads) ; d, nucleus now occupied by double filaments ; e, double chromo- 

 somes ; /, resting vesicular stage of nucleus in which the network is re-established. 



shown that in the synaptic phase the chromatin threads or loops fuse in pairs, thus pro- 

 ducing reduction in the number of chromosomes. Sutton showed in 1902 that there is a 

 certain order in the fusion, leading to the suggestion that the maternal and paternal 

 chromosomes present by hypothesis as persistent individuals in all the somatic nuclei 

 resulting from the fusion in fertilisation of the male and female germ-nucleibecome fused 

 in pairs. The double-rod prophase figure therefore represents not a longitudinally split 

 chromosome, but two chromosomes, one paternal, the other maternal, and the first maturation 

 division separates the paternal from the maternal. 1 It follows that of the four products of 

 the two maturation divisions, two possess paternal and two maternal rods. 



This new idea of reduction of hereditary qualities is different from that of Weismann, but 

 equally well accounts for a redistribution of hereditary attributes (represented by the chromatin) 



1 In some forms it may be that the actual separation takes place in the second division ; the result 

 is the same. 



