No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 
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pas que les differences constatees dans la forme de la tache 
germinative ne doivent etre attribues a la contractility de la 
substance des nucldoles.” The vacuoles in the nucleoli are 
probably “le rdsultat de bunion momentanee de certaines 
parties de la substance nucleolaire avec le sue nucleaire.” 
Before its disappearance the nucleolus breaks into fragments, 
which then dissolve in the “ substance nucldaire.” In this 
fragmentation one fragment is always larger than the others, 
and contains the vacuole of the primitive nucleolus; it persists 
until all the smaller fragments have disappeared. 
Biitschli (’76) found that the nucleolus disappears before the 
formation of the first pole spindle in Tylenchus, Anguillula , 
Notommata , Brachionus , Triart lira, Aphis. He mentions that 
von Siebold, in 1848 , first introduced the name “nucleolus ” for 
the micronucleus of the Infusoria , and compared it with the 
nucleoli of metazoan cells. He also cites some of the earlier 
writers who compared the pole bodies with nucleoli. 
O. Hertwig (’76) calls the nucleolus “das wichtigste Form- 
element des Kerns,” and terms its substance “ Kernsubstanz ” 
in opposition to the “ Kernsaft ” (compare his brother’s paper 
of the same year). In the process of maturation he holds that 
“der Eikern der aus dem Keimblaschen frei gewordene oder 
ausgewanderte Keimfleck ist.” He noticed vacuoles in, but not 
amoeboid movements of, the germinal spot of Toxopneustes 
lividus; he observed such motions, however, in the germinal 
spots of Rana and Pterotrachea. 
R. Hertwig (’76) terms the dense substance of the nucleolus 
“ Kernsubstanz.” “ Entweder leiten sich die vielen Kern- 
korper direkt aus dem homogenen Zustand des Kernes ab, 
indem die Aussonderung der Kernsubstanz an verschiedenen 
Punkten gleichzeitig begonnen hat ; oder die zahlreichen 
Nucleoli sind, . . . durch Theilung aus einem urspriinglich 
einfachen Nucleolus entstanden.” He believes that the 
“ Nucleoli die Trager der Kernfunction sind. . . . Somit 
miissen wir in alien den Fallen, in denen sich ein oder mehrere 
Nucleoli im Kerne differenziren, in diesen die Thatigkeitscen- 
tren des Kernes erblicken.” 
Schwalbe (’76) studied the nuclei of retinal ganglion cells of 
