462 ROBERT W. HEGNER 



or more kinds of bodies are spoken of as nucleoli. Of these may- 

 be mentioned (1) 'the true nucleoli or plasmosomes, (2) karyo- 

 somes or chromatin-nucleoli, and (3) double-nucleoli consisting 

 of usually a single principal nucleolus (Hauptnucleolus of Flem- 

 ming) and one or more accessory nucleoli (Nebennucleoli of Flem- 

 ming) . Many nucleoli have been described which may perhaps 

 represent intermediate stages in the evolution of one of the types 

 mentioned above into another. 



The young ovarian egg of most animals contains a single spheri- 

 cal nucleolus ('Keimfleck,' or germinal spot) but the number 

 may increase greatly during the growth period. Usually during 

 the formation of the first maturation spindle the nucleolus 

 escapes from the nucleus into the cytoplasm where it disappears, 

 often after breaking up into fragments. Many theories have 

 been advanced regarding the origin, function and fate of the 

 nucleoli of the germinal vesicle. They are considered by some of 

 chromatic origin, arising as an accumulation of the chromatin 

 (Retzius, '81; Mertens, '93; Foot and Strobell, '11; Payne, '12, 

 and many others), or from the chromatin by chemical transfor- 

 mation (Schneider, '91; Obst, '99). Others consider them extra- 

 nuclear in origin (Montgomery, '99). 



Many functions have been attributed to the nucleoli; of these 

 the following may be mentioned: (1) They function as excre- 

 tory organs (Balbiani, '64; Bohm, '88; Hodge, '94; Bambeke, '97). 

 (2) Nucleoli play an active role in the cell, since they serve as 

 store-houses of material which is contributed to the formation 

 of the chromosomes (Flemming, '82; Korschelt, '95; Lubosch, 

 '02; G. T. Hargitt, '09; Jordan, '10; Foot and Strobell, '11) 

 and may give rise to kinoplasm (Strasburger, '95) or 'Kineto- 

 chromidien' (Schaxel, '10). (3) Nucleoli are passive by-products 

 of chromatic activity; they become absorbed by active substances 

 (Haecker, '95, '99). (4) Nucleoli represent nutritive material 

 used by the nucleus into which it is taken from the cytoplasm 

 (Montgomery, '99). 



Undoubtedly the various bodies known as nucleoli -originate 

 in different ways, have different histories and execute different 

 functions. 



