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 
