Katharine Foot and E. C. Strobell 211 



Wheeler in Myzostoma, '97, finds that the nucleolus persists in some 

 cases later than the second cleavage but he does not identify any accessory 

 nucleoli. 



The accessory nucleolus of AlJolohopliora probably corresponds to the 

 second nucleolus, Gatliy, '00, describes in Tub if ex as arising indepen- 

 dently and disappearing later than the first. Gathy, however, does not 

 interpret the nucleolus he sometimes finds persisting until the metaphase 

 of the first spindle as the above mentioned second nucleolus. His de- 

 scription of the gradual disappearance of the nucleoli without fragmenta- 

 tion is supported by our observations on the principal nucleolus of dried 

 germinal vesicles (Photos. 121, 122, 123 and 12-4, Plate VIII), though 

 after fixatives the nucleolus is sometimes seen breaking up into frag- 

 ments (Photos. 20, Plate I, 31, 39, 41, Plate II, 54, 55, 57, 67, Plate III, 

 75, Plate IV and 97, Plate V). Dried preparations clearly demon- 

 strate that the principal nucleolus gradually loses its capacity to stain, 

 decreases in size and -finally disappears while the membrane (rf the 

 germinal vesicle is still intact (Photos. 114, Plate VII, 121 to 124, Plate 

 VIII). It does not pass out into the cytoplasm there to degenerate as 

 observed in oocytes in many other forms. This suggests that its func- 

 tional value is confined to the nucleus, and if our interpretation is cor- 

 rect that there is no fundamental difference between the principal 

 nucleolus and the accessory nucleolus we cannot accord any special 

 significance to the fact that the accessory nucleolus, unlike the principal 

 nucleolus, persists in the cytoplasm before its final disappearance. Its 

 cytoplasmic destiny may be due merely to the fact of its later origin and 

 consequently later disappearance, i. e., after the germinal vesicle has 

 been replaced by the spindle. Dried germinal vesicles indicate that a 

 single accessory nucleolus is typical of normal oocytes. Sections of fixed 

 eggs indicate that the single accessory nucleolus owes its origin to the 

 fusing of several smaller ones. 



Many authors have recognized a more or less radical difference between 

 the large nucleolus of the germinal vesicles and the nucleoli of the cleav- 

 age stages, AlJolohopliora does not show the difference between the two 

 nucleoli that Korschelt, '95, indicates for Ophryotroclia. In both Anne- 

 lids the large nucleolus contributes nothing to the formation of the 

 chromosomes, but in Ophryotroclia the cleavage nucleoli " vielleicht ein 

 Theil des vorher im Kernkorper niedergelegten Ghromatins dem Kern- 

 faden beigefiigt wird."' He adds '•' Was die erwahnten Verschieden- 

 heiten des verhaltens der nucleolen in dem Ei- und Embryonalzellen 

 betrifft so liessen sich diese vielleicht durch die recht verschiedenartige 



