3l8 LESTER -W. SHARP 



DISCUSSION. 



llte splittiug of the chromosomes. 



In dealing with this question the following facts, described in détail 

 in the foregoing section, must be borne in mind. At telophase the chromo- 

 somes become transformed into irregular reticulate bands (pages 3o4-3o6), 

 which remain connected as a continuons network through interphase or 

 more complète rest (pages 3o8-3ii), and which again separate from each 

 other at prophase (pages 3ii-3i2). Each then condenses in an irregular 

 manner and gives rise to a thin zigzag thread (page3i2). After this be- 

 comes equalized the longitudinal split occurs through médian vacuolization 

 (page 314), the split so formed remaining until the séparation of the daughter 

 chromosomes at metaphase (page 3 16). 



The point of greatest importance lies in the relation of the vacuoliza- 

 tion which brings about the split to the vacuolization of the preceding 

 telophase. Since there is good reason to regard the vacuoles and subséquent 

 open spaces of the telophase as continuons with those of the early propha- 

 sic bands, the objection might be raised that the later true splitting of the 

 thin threads merely represents a reappearance of the early prophasic spa- 

 ces after the processes of condensation and equalization hâve been accom- 

 plished. This would mean that the splitting is really initiated by the 

 vacuoles of the telophase. That there is no room for such an objection is at 

 once obvions from a careful considération of the détails. During the con- 

 densation of the chromatic matter around the open spaces and occasional 

 vacuoles the thin boundaries of the latter became broken down, leaving a 

 simple but very irregular thread, as has been described at page 3i2. It is 

 clear in the light of thèse facts that thèse spaces and vacuoles in no way 

 enter into the later vacuolization and splitting of the thin thread. It is 

 true that a small vacuole of the early stages might remain at the center of 

 the condensing portion and thus be "used ^ in the later true splitting, but 

 this has not been observed with certainty in any case. The true split, then, 

 which arises through the vacuolization of the thin thread, is a new thing 

 in no way directly connected with the alveolization at the preceding telo- 

 phase. in the explanation of stages absent from other accounts of Vicia 

 we believe to hâve shown conclusively that the true sjjlitting of the chro- 

 mosomes is in this form a prophasic phenomenon. 



