No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 479 



undergoing a degeneration. Quite frequently a small spherical 

 granule lies in the center of the nucleolus and this always 

 stains more intensely than the surrounding substance (Figs. 

 99-102). In only about half a dozen cases, out of hundreds of 

 cells examined, did I find attached to the surface of the nucleo- 

 lus one or two much smaller bodies, which also stained less 

 intensely (Figs. 100 and 10 1). Can it be that in certain cases 

 the nucleolus becomes differentiated into a " Hauptnucleolus " 

 and a " Nebennucleolus," in which case these small bodies 

 would represent the " Nebennucleoli" .■* In certain of the cir- 

 ratida of a young individual the nucleoli of the greater num- 

 ber of nuclei were situated at that pole of the nucleus directed 

 towards the median axis of the cirratidum, i.e., those in the 

 nuclei on the right side of the cirratidum were in the left-hand 

 poles of the nuclei, and thdse in the nuclei of the left side of 

 the cirratidum (as seen on sections) were placed at the right- 

 hand poles of the nuclei. I did not observe this regular posi- 

 tion of the nucleoli in the cirratida of the other individuals 

 sectioned and hence would conclude that it was not a normal 

 phenomenon, but an osmotic consequent of the fixing reagent.^ 

 The size of the nucleolus preserves approximately the same 

 ratio to that of the nucleus. 



The nucleus is either spherical or oval in outline. The 

 apparent arrangement of the chromatin varies according to the 

 fixative employed. After picro-nitro-osmic acid (Fig. 102) it 

 appears granular; after Hermann's fluid (Figs. 99-101), in the 

 form of delicate fibers which radiate from the nucleolus to the 

 nuclear membrane ; after alcoholic solution of corrosive subli- 

 mate (Fig. 98) we find a few fibers radiating from the surface 

 of the nucleolus, but the greater amount of the chromatin 

 appears in the form of granular masses, which lie mainly near 



^ In a previous paper ('96) I figured for the nuclei of those mesenchym cells 

 which surround the distal end of the ventral nerve cords of Cerebratulus lacteus, 

 the nuclei with their chromatic masses pressed against that side of the nuclear 

 membrane which was situated nearest to the central point of the section. At 

 that time, I regarded this excentric position of the chromatin as a normal but 

 peculiar phenomenon ; but now, on comparison with the cells of Doto, I am 

 convinced that it is an artefact produced by the osmotic action of the fixing 

 reagent. 



