No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 32 1 



a smaller mass of chromatin, or at least of a substance which 

 does not differ in its reactions from the chromatin of the coiled 

 filaments in the same nuclei." This nucleolus divides first 

 in mitosis. 



i8go. 



Auerbach ('90) distinguished two kinds of chromatin sub- 

 stance : " erythrophile," 2>., substances staining with eosin, 

 fuchsine, aurantia, carmine, picrocarmine ; and " kyanophile," 

 substances staining with methyl green, aniline blue, haematoxy- 

 lin. The nuclear reticulum is not the fundamental portion of 

 the nucleus, but the nucleoli are its important elements. He 

 finds " dass in einer Grundsubstanz, die im frischen Zustande 

 homophan, im geharteten . . . hbchstens feinkornig erscheint, 

 grossere, scharf begrenzte, isolirte, starker lichtbrechende und 

 starker farbbare Korperchen, Nucleoli, von wechselnder.aber fur 

 die verschiedenen Zellarten und Thierspecies typischer Anzahl 

 eingebettet sind"; thus in the Batracliia most of the nuclei 

 contain numerous nucleoli, and when they are particularly 

 abundant the greater number are peripheral in position. 

 There are two kinds of " Kernkorperchen," those which stain 

 blue (or green) and those which stain red (or yellow) ; both 

 kinds occur in most nuclei. In the giant nuclei of the gland 

 cells from the skin of Urodelca are found (i) numerous small cyan- 

 ophilic nucleoli, and (2) from one to fifteen (usually two to five) 

 much larger, erythrophilic nucleoli, which sometimes contain vac- 

 uoles. Embryonal nuclei contain only cyanophilic nucleoli, while 

 in maturer nuclei erythrophilic nuclei become differentiated 

 from the former. Thus in the blood corpuscles of frog larvae 

 there is at first only one large nucleolus, which later differenti- 

 ates into an inner erythrophilic and an outer cyanophilic por- 

 tion. The peripheral layer next breaks up and divides into 

 small cyanophilic nucleoli, while the central portion remains 

 as a large erythrophilic nucleolus. Subsequently the smaller 

 cyanophilic nucleoli (" Nebenkiigelchen ") may fuse together 

 so as to produce six or eight larger cyanophilic nucleoli, each 

 of which attains the size of the original " Stamm-Nucleolus"; 

 at the conclusion of the larval period of the frog, the latter 



