58 



CYTOLOGY 



CHAP. 



reaction, appearing indeed to consist now entirely of achromatin or 

 oxy chromatin. At the same time the number of nucleoli increases. 



At the end of the growth period the chromosomes undergo a reverse 

 process of concentration, the filamentar outgrowths being apparently 



Fig. 22. 



stages in the oogenesis of the dog-fish, Pristiurus. (After Mare'chal, L.C., 1907.) A, pachytene stage, 

 nucleolar mass already conspicuous ; B, C, passage of the diplotene stage into the germinal vesicle. In C 

 the number of nucleoli has increased. D, early stage in the reconstruction of the chromosomes ; E, F, later 

 stages in the condensation of the chromosomes into the definitive bivalents. These two figures are drawn 

 at the same magnification. 



c, chromosome ; n, nucleolar filament. 



retracted on to the central axis. At the same time the staining capacity 

 of the chromosomes increases again, and they diminish enormously in 

 size. The nucleoli break up, and their substance shows evidence of 

 degenerative changes, forming small granules or droplets. Sometimes 

 these get arranged one behind the other into filaments superficially not 

 ' unlike chromosomes (Fig. 22, D) but having in reality no relation to these. 



