No. 2 .] COMPARATIVE CYTOLOGICAL STUDIES. 285 
lus is absent, in others there is a single one, sometimes with 
a vacuole; in the Choanojiagellata there is always one large, 
spherical nucleolus, in the Cystojlagellata several of various 
sizes; and in the Dinojiagellata there may be several small 
nucleoli, which are sharply localized from the chromatin, but 
show the fine reticulation of the latter element. In the Ciliata 
and Suctoria there are nucleoli of varying size and number in 
the macronucleus, but none in the micronucleus. 
Chun (’ 80 ) finds in the egg of all Cte7iophora a single large 
nucleolus, very rarely two. 
Engelmann (’ 80 ) figures the nucleoli of certain ciliated cells 
of various invertebrates as each surrounded by a clear space, 
the outer boundary of which is marked on optical cross-section 
by a circle of granules. 
Flemming (’80) concludes in regard to the nature of the 
nucleolus: “ Dass die Nucleolen iiberhaupt keinerlei mor- 
phologischen Antheil an der Kernvermehrung nehmen”; and 
“ Dass die Dinge, die wir Nucleolen nennen, vielleicht gar keine 
morphologisch wichtige Theile des Kerns, sein mogen, sondern 
nur Ablagerungen von Substanzen, welche fur den Stoffwechsel 
im Kern verbraucht und wieder neugebildet werden; sie wiirden 
damit gewiss physiologisch wichtige Theile des Kerns bleiben, 
— was ohnehin durch ihr fast allgemeines Vorkommen bewahrt 
wird, — aber doch keine eigentlich organischen, d. h. morpholo- 
gisch-wesentlichen Kernbestandtheile.” 
O. Hertwig (’ 80 ) found in the eggs of Chaetognatha numerous 
small nucleoli. 
Shafer (’ 80 ), ovum of Gallns: there is a single nucleolus, 
which in young germinal vesicles consists of a homogeneous 
matrix which stains slightly with haematoxylin, and a number 
of coarse granules which stain deeply; in larger ova the 
nucleolus is homogeneous throughout and stains deeply. The 
threads radiating from the periphery of the nucleolus may be 
either artefacts or may be regarded as extrusions of the homo¬ 
geneous substance of the nucleolus. Ovum of Lepus: in 
younger nuclei the nucleolus has the same general structure 
as in the fowl, though it is more irregular in form. In some 
larger ova the nucleolus “ is represented by a number (a dozen 
