No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 513 



losungsvorgange," due to chemical changes in its substance. 

 Cf. the movements described by Flemming ('97) for the ovum 

 of Ascidia. 



The nucleolus has in some cases a viscid consistency {as 

 described by me for Stichostomna) and then may be irregular 

 in form ; in other cases it is more fluid, and this is probably 

 the case when it has regularly a spherical shape, i.e., the globu- 

 lar form characteristic of drops of a thin liquid. Its more or 

 less fluid consistency allows changes of form, division into 

 particles, and fusions of neighboring nucleoli. 



The division of a nucleolus into two or more parts is a 

 normal and regular phenomenon in many cells, though all 

 nucleoli do not show this property. Two kinds of nucleolar 

 division may be distinguished : (i) that mode by which the 

 nucleolus becomes elongated and then breaks into two or more 

 parts, whereby the daughter-nucleoli are usually capable of 

 further division ; and (2) that mode by which the nucleolus 

 fragments nearly simultaneously into a number of small gran- 

 ules. From my own observations the former mode is evinced 

 by the nucleoli of the muscle and giant gland cells of Piscicola, 

 the giant cells of Doto, and the germinal spots at certain 

 stages in the ovogenesis of the metanemerteans. This mode of 

 division cannot be regarded as a phenomenon of nucleolar 

 degeneration, since the nucleolus and its products may often 

 continue to increase in size during the process of division. But 

 the second mode, that by which the nucleolus breaks into a 

 large number of granules, since it is particularly characteristic 

 of the nucleolus in nuclear division, may be regarded as a 

 process of degeneration ; the case of divisions during nuclear 

 division shall be considered later, A strange mode of nucleolar 

 division has been described by A. Schneider ('83). According 

 to his observations on Klossia, the smaller nucleoli are portions 

 of the inner substance of the larger nucleoli and wander out of 

 each larger one by passing through the pore (" canal micropy- 

 laire ") of the cortical substance of the latter; this intranucleolar 

 origin of the smaller nucleoli is still open to question, since it 

 was not observed in life, and since the canal micropylaire was 

 observed in only one nucleolus. Marshall ('92) has described 



