SIGNIFICANCE OF NUCLEAR CHANGES 21. 



the oocyte became a functional ovum. Weismann's theory, very briefly put, postulated a 

 qualitative reduction of the hereditary substance, brought about by a transverse cleavage 

 of the chromatin-rods, the halves of which were separated in the second division, the rods or idants 

 by his hypothesis being organised into lower-grade groups of the ultimate particles of the heredi 

 tary substance (ids and determinants). During more than a decade of research to which this 



6 c 



FlG. 30. FlGUBES ILLUSTRATING BEHAVIOUR OF CHROMOSOMES DURING MATURATION DIVISION. 



a, Metaphase of heterotypical division, spermatocyte i. of Batrachoseps (Eisen) ; b, anaphase of 

 heterotypical division in spermatocyte i. of Salamandra, showing secondary cleavage of chromosomes ; 

 c, metaphase of homotypical division, spermatocyte 11. of Salamandra (Meves). 



hypothesis gave rise, the evidence for and against its actual realisation in fact was pretty equally 

 divided. The cases in which the two maturation chromosomal cleavages seemed both to be 

 longitudinal, resulting therefore in an equal distribution of the chromatin-mass to the quaternary 

 group of gametes, were supported by as cogent evidence as those in which the splitting was 

 described to be once longitudinal and once transverse, as was necessary for the idea of an 

 unequal distribution of the supposed hereditary substance. So great was the contradiction 



