CHAPTER V 



OOGENESIS AND SPERMATOGENESIS. REDUCTION OF THE 



CHROMOSOMES 



" Es komnit also in der Generationenreihe der Keimzelle irgendwo zu eiiier Reduktion 

 der urspriinglich vorhandenen Chromosomenzahl auf die Hiilfte, und diese Za/iUn-reduk- 

 tion ist demnach nicht etwa nur ein theoretisches Postulat, sondern eine Thatsache." 



BovERl.i 



Van Beneden's epoch-making discovery that the nuclei of the con- 

 iuo-atinsf srerm-cells contain each one-half the number of chromosomes 

 characteristic of the body-cells has now been extended to so many 

 plants and animals that it may probably be regarded as a universal 

 law of development. The process by which the reduction in number 

 is effected, forms the most essential part of the phenomena of uiatui-a- 

 tion by which the germ-cells are prepared for their union. No phe- 

 nomena of cell-life possess a higher theoretical interest than these. 

 For, on the one hand, nowhere in the history of the cell do we find so 

 unmistakable and striking an adaptation of means to ends or one of 

 so marked a prophetic character, since maturation looks not to the 

 present but to the future of the germ-cells. On the other hand, the 

 chromatin-reduction suggests problems relating to the morphological 

 constitution of nucleus and chromatin which have an important 

 bearing on all theories of development, and which now stand in 

 the foreground of scientific discussion among the most debatable 

 and interesting of biological problems. 



It must be said at the outset that the phenomena of maturation 

 belong to one of the most difficult fields of cytological research, and 

 one in which we are confronted not only by diametrically opposing 

 theoretical views, but also by apparently contradictory results of 

 observation. 



Two fundamentally different views have been held of the manner 

 in which the reduction is effected. The earlier and simpler view, 

 which was somewhat doubtfully suggested by Boveri i^'&'J, i ), and has 

 been more recently supported by Van Bambeke ('94) and some others, 



1 Zelleiistudien, III. p. 62. 

 173 



