No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 
539 
plasmatiques ” of Carnoy, and the “ Plasmosomata ” of the 
other observers correspond to true nucleoli in the sense in 
which this term should be used. The existence of Carnoy’s 
“ nucleoles mixtes ” and “ nucleoles-noyaux ” in cells of Metazoa 
appears to be doubtful. List (’96) considers that the paranu- 
cleoli of the egg cells and the nucleoli of the somatic cells 
are homologous, but that the nucleolus proper of the ova 
is different from both; but the chemical differences which he 
finds between these kinds of nucleoli do not prove that they 
are morphologically distinct structures. 
Appendix to the Literature Reviews. 
Siebold (’39) noticed “ in den Eiern von Plumatella campanu- 
lata Lam. . . . ein deutliches Keimblaschen mit gedoppeltem 
Keimflecke.” 
Koelliker (’43) concludes : “ Es bestande . . . das Ei aus 
einer primitiven Zelle, dem Keimblaschen, die sich um einen 
Kern, den Keimfleck, gebildet, und um die sich nachher Korner 
und eine secundare Zelle, die Dotterhaut, gelegt hatte.” 
Auerbach (’74a) was the first to emphasize and prove clearly 
that the number of nucleoli is usually quite large, and that they 
are frequently irregular in form (before this time it was generally 
assumed that the usual number of nucleoli was one or two). 
The nucleus is filled with “ Grundsubstanz ” (the “ Zellsaft ” of 
Kolliker) and “ Zwischenkornchen ” ; the latter are distin¬ 
guishable from the nucleoli by their smaller size and different 
refraction. He explains the clear zone around the nucleolus 
and the “ Kernkorperchenkreis ” of Eimer by the action of a 
repulsive force on the part of the nucleolus and of the nuclear 
membrane. He distinguishes several successive stages of the 
nucleus with regard to the number of the nucleoli : enucleolar 
nuclei, at an early embryonal stage ; paucinucleolar nuclei, 
with one or two nucleoli ; pliirinucleolar nuclei, with two to four ; 
and multinucleolar , with more than four. “ Die Zahl der Kern- 
korperchen in einem Kerne betragt 1 - 16 , und in extremen 
Fallen selbst noch viel mehr, bis fiber 190 . Und zwar ist nur 
eine kleine Minderheit aller Kerne durch den Gehalt von nur 
