No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 533 



nucleolus. Bohm described ("88) the vacuole of the germinal 

 spot of Petromyzon as connected by a fine duct with the sur- 

 face of the nucleolus. Lukjanow ('88) found in the stomach 

 cells of the salamander that the nucleolus is apposed to the 

 nuclear membrane, through which it discharges an excretion. 

 Compare also Van Bambeke ('97a) and Michel ('96). These 

 observations would show that the nucleolus in some cases con- 

 tains a contractile vacuole, and that the fluid substance of the 

 latter is periodically discharged from it {cf. Hodge '94, Van 

 Bambeke, '97, and Michel, '96). 



Flemming ('82) considers the nucleoli to be nuclear organs, 

 and regards them either as containers or reserve supplies of 

 chromatin, or as " eine chemische Modification, Vorstufe oder 

 Doppelverbindung " of the latter substance ; this view is also 

 held by Van Bambeke ('85). Zacharias ('85) also thinks that 

 they are organs, but does not agree with Flemming that they 

 are reserve masses of chromatin; Gjurasin ('93) corroborates 

 the views of Zacharias. Strasburger originally contended ('84) 

 that they represent reserve material, a view shared by many 

 later observers ; more recently ('88) he shows that the nucleolar 

 substance may play some part in the formation of the cell 

 membrane, but considers that they may also have some other, 

 as yet unknown, function. Korschelt ('89) concludes that they 

 are formed as depositions of nutritive substances, and that their 

 substance " in und vielleicht ausserhalb des Kernes zur Ver- 

 wendung gebracht werden sollte." Rhumbler ('93) assumes 

 that the nucleoli (" Binnenkorper ") of the Protozoa represent 

 " Reservestoffe " deposited in the nucleus and consumed in 

 the growth of the latter, standing in some connection with the 

 chromatin ; they are not organs, but secretions of the nucleus. 

 Hacker ('95) concludes that they are not nuclear organs, but 

 secretions of the nucleus formed in or from the chromatin 

 elements and destined to be discharged from the nucleus dur- 

 ing mitosis; he observes that the nucleolar substance "ein 

 Stoffwechselsprodukt darstellt, dessen Erzeugung in einem 

 gewissen Abhangigkeitsverhaltniss zur Intensitat der vegeta- 

 tiven Leistungen von Kern und Zelle steht," and that its amount 

 stands in a direct ratio "zur Intensitat der Wechselbeziehungen 



