No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 389 
or spherical, and after haematoxylin-eosin, stain a rose color, 
while the chromatin is blue. At the time of the appearance of 
the chromosomes, “ treten die Nucleolen aus den sich zusam- 
menordnenden Plasma und lassen sich hier in Form scharf 
umschriebener, homogener, roth gefarbter Kiigelchen nach- 
weisen.” Usually two nucleoli wander out, at least never more 
than two were found outside of the nucleus. These two come 
to lie at opposite poles of the nucleus, occupying the positions 
of centrosomes; and when the longitudinal splitting of the 
chromosomes takes place, each of the nucleoli also divides into 
two. Karsten believes these nucleoli are identical with the 
centrosomes of Guignard; but he does not explain what becomes 
of the third nucleolus during the division. 
Lauterborn (’93), quoted by Karsten (’93), diatoms : there 
is a centrosome lying in a concavity of the nucleus; he noticed, 
further, “ beim Beginn der Theilung aber zwischen Kern und 
Centrosom noch ein anderes Gebilde —, welches im spateren 
Verlauf der Karyokinese eine sehr bedeutsame Rolle spielt, 
namlich die Anlage der Centralspindel ”; this body must be 
derived either from the nucleus or the centrosome (I mention 
it here since it may in the future be found to have some con¬ 
nection with a nucleolus). 
Moll (’93) studied karyokinesis in Spirogyra. There are one 
or two nucleoli, which stain more intensely with gentian violet 
than any other portion of the nucleus. They may be vacuolar 
in structure, or contain a skein of chromatin ; they appear 
homogeneous only when too deeply stained. The skein struc¬ 
ture (the skein itself staining as chromatin) is found in resting 
nuclei, as well as in the prophases of mitosis, and at the same 
time vacuoles may be present. He assumes that the thread in 
the nucleolus contains all the chromatin of the resting nucleus, 
and “ that by the nucleolus the chromatin substance for the 
segments [chromosomes] is furnished”; this chromatin leaves 
the nucleolus in mitosis, and “ it seems as if the chromatic sub¬ 
stance were squeezed from the nucleolus by an aperture.” After 
the chromatin skein has left the nucleolus, the latter disappears. 
(Strasburger’s paper, ’93, was reviewed under the head of 
zoological literature.) 
