No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 
and the third kind, which occur in the embryo sac, “ are not 
present in the mitotic nucleus, but in the retrogressive stage 
[metaphase] they appear on the course of the filaments as 
spherical elements enclosing one or more refracting corpuscles 
and containing but a small amount of iron, which, however, in 
later stages ... is more abundant. These nucleoli are eventu¬ 
ally formed chiefly of chromatin, and in stained preparations 
appear to contain nearly all the chromatin of the nucleus. 
When mitosis again commences the filament forms at their 
expense, the increase in size of the filament keeping pace, 
apparently, with the decrease in the quantity of chromatin 
which the nucleoli contain. Finally, before their disappearance, 
when they contain but a minimal quantity of iron, they take 
the eosin stain deeply. All these forms of nucleoli take up 
safranin from solutions as readily as do the chromatin elements 
in the same nuclei, and they hold the stain as tenaciously when 
they are washed with alcohol. They are in this respect differ¬ 
ent from the eosinophilous nucleoli in the animal cell, which 
appear to be unrepresented in the vegetable cell.” In Spirogyra 
and Corallorhiza “ the greater portion of the chromatin in each 
nucleus forms a single large spherical element unconnected with 
the chromatin network.” He corroborates Leydig’s view of 
the structure of the chromatin loops in the nuclei of the salivary 
glands of Chironomus; the nucleolus is often vacuolar and 
amoeboid, and may be transversed several times by the chro¬ 
matin loop ; “ the presence of granules and vacuoles . . . 
appears to indicate that it is physically active, which cannot be 
postulated of the vast majority of the nucleoli of Vertebrate 
cells.” In Euglena the nucleolus stains deeply with eosin 
(except after fixation in picric acid), but does not stain with 
safranin ; it is “ intermediate in composition between the nucle¬ 
olus of higher animal cells and the chromatin of the nuclear 
reticulum.” 
Mead (’95), egg of Chaetopterus: “in the second cleavage, as 
in the first, the nucleoli are dropped out into the cytoplasm in 
the equatorial plane.” 
Montgomery (’95) described the various arrangements of the 
nucleoli (“ Chromatinmassen ”) in the ova of Stichostemma 
