No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 515 



process is to some extent dependent upon the nature of the 

 medium in which they are suspended (cf. Rhumbler, "93). {Cf. 

 also Hermann, '89b ; Bouin, '97 ; Mertens, '93 ; Debski, '97 ; 

 Carnoy and Lebrun '97a ; Koernicke, '96.) 



7. Paranucleoli and Pseudonucleoli, Double Nucleoli, etc. 



The term paranucleolus is here adopted as equivalent to 

 Flemming's " Nebennucleolus," and I shall use simply the 

 name "nucleolus," or "nucleolus proper," instead of " Haupt- 

 nucleolus." E. B. Wilson's terms, "principal nucleolus" and 

 " accessory nucleolus," are somewhat inconvenient on account 

 of their length, and may be misleading, since the " principal 

 nucleolus" is often smaller than the "accessory nucleolus." 

 "Paranucleolus," as used here, is not employed in the same 

 sense as by Stuhlmann ('86), since he expresses by this term 

 portions of the nuclear reticulum ; in my paper the term 

 " nucleolus " has not been used for any part of the chromatin 

 elements of the nucleus. 



In many egg cells, especially those of the Mollusca, Annelida, 

 Tunicata, and Echinodermata, two kinds of nucleoli occur accord- 

 ing to the writers on these objects, which differ from one 

 another chemically and in some cases also structurally ; these 

 are the nucleolus proper and the paranucleolus. Of these it 

 is the nucleolus proper which seems to be morphologically 

 comparable to the nucleoli of somatic cells, however the two 

 may differ chemically. The paranucleolus may be either larger 

 or smaller than the nucleolus, and appears usually to be distin- 

 guishable from the latter by staining less deeply with the 

 specific nucleolar stains. In the spermatoblast of the mouse 

 these two kinds of nucleoli have been found by Hermann ('89) ; 

 and in somatic cells by Lonnberg ('92, liver cells of Doris, Poly- 

 cera, Aeolidia, and Astacus) ; perhaps the smaller of the two 

 nucleoli found by me in the blood corpuscles of Doto might 

 represent a paranucleolus. In plant cells apparently only one 

 kind of nucleolus is present, this being comparable morphologi- 

 cally to the nucleolus proper of the germ cells and to the nucle- 

 oli of the somatic cells of Metazoa. Thus paranucleoli are quite 



