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[Vol. XV. 
substance during the following mitosis ; wherefore he suggests 
the term “ Prochromatin ” for nucleolar substance. In the pro¬ 
phase of the mitosis only one nucleolus is present in the 
nucleus, while in the “ Riickkehr der Tochterkerne zum Ruhe- 
stadium waren dagegen stets mehrere vorhanden. In einem 
gewissen Stadium, wo die Nucleolenbildung beginnt, ist eine 
ganze Anzahl vorhanden ; jemehr sich der Tochterkern dem 
Ruhestadium nahert, desto mehr vermindert sich die Zahl 
unter gleichzeitiger bedeutender Grossenzunahme der iibrigge- 
bliebenen, bis fur das ausgesprochenste Ruhestadium das Vor- 
handensein eines einzigen grossen central gelegenen Nucleolus 
geradezu typisch wird,” and this he concludes to be a process 
of fusion. The nucleolus plays only a passive role in mitosis, 
“namlich die eines aufgespeicherten Nahrungsmaterials zur 
Neubildung von Chromatin.” 
Rein (’ 83 ) studied the eggs of Lepus and Cavia. In each 
there is one large nucleolus which disappears during matura¬ 
tion and is succeeded by several smaller ones, which have the 
same consistency as the first, and at the time of their first 
appearance occupy a central position in the nucleus. “ So weit 
ich den Vorgang am Saugethiere verfolgen konnte, machte mir 
derselbe eher den Eindruck eines successiven Zerfalles des 
urspriinglichen Keimflecks in immer kleinere Stiickchen, welche 
schliesslich in der Substanz des Keimblaschens verschwinden.” 
Route’s (’ 83 ) conclusions are, in the main, confirmatory of 
Fol’s (’ 83 ) observations in regard to endogenous cell formation. 
In the egg of Ciona there is one large and two or three smaller 
nucleoli, the latter being “ formes pendant revolution des 
cellules endotheliales en cellules ovulaires.” In eggs a little 
larger these “nucleoles adventifs ” become more numerous (five 
to six), and certain of them show a limiting membrane. Later 
still some of these adventive nucleoles are found in the yolk, 
where each becomes surrounded by a clear zone; these he con¬ 
siders at this stage to be the nuclei of endogenetically formed 
cells (follicular cells), the clear zone around each representing 
its cytoplasm. 
Schauinsland (’ 83 ) noticed in the egg of Distomum a single 
large nucleolus. 
