No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 357 



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 Chironovms ; 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), &^^g 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 



