1 68 Gardner — SUidics on Grozvth and Cell 



two or more parts whereby the daughter nucleoH are usually- 

 capable of further division, and (2) the mode in which the 

 nucleolus fragments nearly simultaneously into a number of 

 small granules. The author regards the second mode as a 

 process of degeneration. 



Fusion of Nucleoli. — This is not as widely known as division, 

 yet it is not unusual. The nucleolus at the time of its origin 

 may be said to be undergoing a process of fusion, since it is. 

 produced by the coalescence of numerous small portions of 

 nucleolar substance. 



Origin of Nucleolus. — In ova of Nemerteans, nucleoli always 

 appear in contact with the nuclear membrane, then wander 

 toward the center. This appearance of the nucleolus near the 

 nuclear membrane is explained by the fact that the nucleolus 

 is extranuclear in origin. The author says he has found no 

 evidence that the nucleoli derive any part of their substance 

 from the chromatin. The nucleus seems to assimilate some 

 substance from the cytoplasm, and after this has entered the 

 nucleus it undergoes a chemical change, and is deposited on 

 the inner surface of the nuclear membrane in the form of 

 masses of varying dimensions. Its origin is extranuclear, 

 and though it may undergo chemical changes after entering 

 the nucleus, it can be regarded neither as an excretion nor a 

 secretion of the latter. 



Behavior of the Nucleolus during Nuclear Division. — During 

 mitosis, the nucleolus may either not disappear or it may dis- 

 appear before the spindle has formed. In cases where it does 

 not disappear, it divides in two, each daughter nucleus receives 

 half. The usual mode of behavior is for the nucleolus to 

 disappear. It either diminishes in size and then vanishes, or 

 it first fragments into a number of smaller pieces which then 

 disappear. The dissolution of the nucleolar substance com- 

 mences before the nuclear membrane has disappeared and by 

 the time it has disappeared all the nucleolar substance is dis- 



