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 mi.xtes " and " nucleoles-noyaux " in cells of Metasoa 

 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 : eniicleolar 

 nuclei, at an early embryonal stage ; paiicinucleolar nuclei, 

 with one or two nucleoli ; pl!iriniiclcolarx\\ic\e\, 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 uber 190. Und zwar ist nur 

 eine kleine Minderheit aller Kerne durch den Gehalt von nur 



