NUCLEOLI IN EUSCHISTUS VARIOLARIUS. 22/ 



In the past, however, similar claims have been made for the 

 centrosome--its individuality and continuity were asserted by 

 many cytologists, some going so far as to believe the centrosome 

 to be the cause rather than the expression of cell activity. 



Certain facts indicate that all the chromatic substance of the 

 germinal vesicle of Enschistus is not used for the chromosomes. 

 We find in many germinal vesicles various segregations of chro- 

 matic substances which are present after the chromosome threads 

 are formed and which often do not entirely disappear until the 

 prophase stage. We sometimes find irregular granular or homo- 

 geneous masses as in Photos 20 and 22, sometimes numerous large 

 granules, so dense that they look like very small nucleoli (Photos 

 19, 21, 23, 26, 27 and 29), and sometimes merely deeply staining 

 areas, as shown in Photos 23, 24 and 27. We have no means of 

 proving that this chromatic substance, not used for the chromo- 

 somes, is chromatin, but for many forms it has been claimed that 

 only a small part of the chromatin is used in the formation of the 

 chromosomes and we are therefore perhaps justified in surmising 

 that the chromatic substance in EnscJiistns (which often persists 

 until after the chromosomes are formed) may be chromatin resi- 

 due, which assumes various forms during its disintegration and 

 disappearance. 



The early stages of the development of the germinal vesicles 

 shown in Photos 1 1 to 1 7 we interpret as indicating that the chro- 

 mosomes completely disintegrate --that any claim of their mor- 

 phological persistence during these stages must be made as a 

 pure assumption, as there is no morphological evidence whatever 

 of their persistence. On the contrary there is every indication 

 that they completely disintegrate. We believe we have no 

 reason to assume that the reappearance of the chromosomes at 

 certain stages differs essentially from the reappearance of the 

 centrosome, aster, spindle, nucleolus and other cell structures. 



Pick ('07) in his critical review of the inconclusive evidence 

 that has been offered as proof of the individuality and continuity 

 of the chromosomes, and of their causal character, sounds a 

 welcome note of protest against recent chromosome specula- 

 tions. In addition to Pick such experienced cytologists as 

 Hacker and Meves, have expressed their skepticism of the sex- 



