No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 387 



and less assimilative albuminoid material than the nucleolar 

 chromatin. On the assumption just stated, we could explain 

 also why we find ... at the time of maturation portions of 

 nucleolar matter detaching themselves from the main nucleolus 

 to undergo a peculiar gelatinous change. The gelatinous change 

 would correspond to a conversion of the assimilative material 

 into achromatic elements, an explanation which would also 

 explain the disappearance of nucleoli during the division of a 

 cell. ... I believe the hypothesis that the nuclear chromatin- 

 segments and perhaps the nucleoli are organs for the conversion 

 of assimilated material into material directly available for the 

 achromatic elements of the cell to be not quite erroneous." In 

 the mechanism of cell conjugation : "The endonuclcolar fibers 

 running through the body-plasm of the two sexual cells . . . are 

 brought into contact with one another whenever the pseudopo- 

 dial processes of the two cells have met. As soon as an union 

 of fibrils has taken place, each fibril will commence to contract 

 similarly to a muscular fibril," which results in drawing the two 

 nuclei, afterwards also the two nucleoli, together ; thus the 

 endonucleolus is the " tropic center " of the cell. 



Rosen ('92a) studied the differential staining of the nuclear 

 elements in plants. Flowers of Scilla : in the nuclei of the 

 " Bijndelparenchym " are numerous large nucleoli, which differ 

 in form and size; the one or two larger ones, " Eunucleoli," are 

 each surrounded by a clear space, but none is present around 

 the smaller " Pseudonucleolen." With the double stain, Alt- 

 mann's acid fuchsine and methylen blue, the Eunucleoli stain 

 red and the Pseudonucleoli blue, or vzcc versa. Similar cells 

 of HyacintliHS : by the application of the double stain, aqueous 

 solutions of fuchsine and methylen blue respectively, the 

 Eunucleoli stain red, the Pseudonucleoli blue ; but when these 

 stains are applied in the reverse order, the nucleoli stain 

 reversely. He considers, following Auerbach ('90), that the 

 Eunucleolus is erythrophilic, the Pseudonucleoli kyanophilic, 

 the latter staining as does the chromatin network. "Meine 

 Pseudonucleolen aber sind eben offenbar weiter nichts, als 

 besonders selbstandig ausgebildete Bestandtheile des chrom:i- 

 tischen Kerngeriistes und sind wie dieses und sein Produkt, der 



