168 Gardner—Studies on Growth and Cell 
two or more parts whereby the daughter nucleoli 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 asa 
process of degeneration. 
Fusion of Nucleoli.—TVhis is notas 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-. 
