528 MONTGOMERY. [Vol. XV. 



explained either by the assumption that the nucleolar substance 

 unites chemically with the chromatin, or that it simply pene- 

 trates into the meshes of the latter ; since no nucleolar 

 substance appears to be united with any of the twelve chromo- 

 somes we may conclude that it does not unite chemically with 

 the chromatin, and therefore the chromosomes probably do not 

 serve to carry it over into the daughter-nuclei. We may now 

 briefly review the results of other observers on the mode of 

 disappearance of the nucleolus during mitosis. 



It is not necessary to discuss the earlier view of O. Hertwig, 

 which he has since discarded, that " der Eikern der aus dem 

 Keimblaschen frei gewordene oder ausgewanderte Keimfleck 

 ist," nor yet the view of Kolliker. Kleinenberg ('72) believes 

 that the germinal spot of Hydra dissolves during mitosis ; 

 Brauer ('91) finds that it breaks into fragments, of which a part 

 seems to be dissolved in the cytoplasm, " ein Theil tritt unver- 

 andert nach dem Schwinden der Membran in das Eiprotoplasma 

 iiber." Pick ('93, germinal spot of Amblystomd) finds that the 

 nucleoli disappear at the time of the longitudinal splitting of the 

 chromosomes ; and Bohm ('88) reaches the same conclusion for 

 Petroinyzon. Davidoff ('89, ovum of Distaplid) concludes " dass 

 aus dem Nucleolus ein Kern mit Kernnetz, mit einem Nucleolus 

 und Nucleolinus hervorgegangen ist " ; and Vejdovsky ('88, 

 RhyncJielmis), Blochmann ('82, Neritina), and Marshall ('92, Gre- 

 garind) conclude that the nucleoli become chromosomes. In the 

 Q%g of Ascaris the nucleoli gradually disappear, according to most 

 observers. Strasburger ('82b) first contended that the nucleolar 

 substance is taken up into the nuclear filaments ; later ('88) he 

 writes : " Auf Grund meiner neueren Erfahrungen erscheint es 

 mir iiberhaupt unwahrscheinlich, dass die Nucleolarsubstanz, 

 auch nach ihrer Auflosung im Kernsafte, den Kernfaden als 

 Nahrung dienen sollte," and he considers that after it is 

 dissolved in the nuclear sap a portion of it forms the cell 

 membranes of the daughter-cells {cf. also his paper of '93). 

 Rein ('83, ova of Lepus and Cavid) finds that the nucleolus 

 breaks into small fragments, which finally disappear in the 

 substance of the nucleus. Pfitzner ('83, ectoderm cells of 

 Hydra) terms the nucleolar substance " prochromatin," since 



