538 MONTGOMERY. [Vol. XV. 



in Protozoa which are unique, such as the nucleolo-centrosome 

 of Keuten ('95). Henneguy considers that the corpuscle of 

 Balbiani, together with the nucleolar elements of the metazoan 

 cell, corresponds to the macronucleus of the Infusoria ; in con- 

 nection with this view may be mentioned the observations of 

 Biitschli ('80), according to which only the macronuclei of the 

 Ciliata contain nucleoli. Henneguy's hypothesis is very ingen- 

 ious, and opens an interesting field for investigation, but it is 

 difficult to determine whether it corresponds to the facts at 

 hand, or whether it does not.^ Some of the nucleoli of Protozoa 

 are comparable to those of Metazoa, but it is doubtful whether 

 all of them are.^ Thus it may be the case in some of the 

 gregarines that the chromatin (or its physiological equivalent) 

 is localized in some or all of the nucleoli, and such structures 

 could not be compared with the nucleoli of the metazoan cell. 

 As to the metazoan nucleoli, there is the question whether 

 the nucleoli of egg cells and of somatic cells should be consid- 

 ered homologous. In my opinion this may be answered in the 

 affirmative, since the nucleoli of both kinds of cells appear to 

 be depositions of substances which are concerned in the nutri- 

 tive processes of the nucleus. In making this conclusion I 

 limit myself to the true nucleoli and do not consider those 

 structures which have been erroneously termed nucleoli, but 

 which in reality are portions of the chromatin reticulum of the 

 nucleus. Numerous writers have considered the thickened 

 nodal points of the nuclear network to be nucleoli, and here 

 may be mentioned Leydig, Klein, Waldeyer, and others. The 

 " cyanophilic " nucleoli of Auerbach ('90), the " pseudonucleoli " 

 of Rosen ('92a), the " nucl^oles nucleiniens " of Carnoy ('85), 

 and the " Karyosomata " of Ogata ('83), Lukjanow ('87b), and 

 Macallum ('9l) are undoubtedly not nucleoli but portions of 

 the nuclear reticulum. While the " erythrophilic " nucleoli 

 of Auerbach, the " Eunucleoli " of Rosen, the " nucl^oles 



1 On the genetic relation of nucleoli to Ealbianian corpuscles (true yolk-nuclei), 

 a relation which seems to me very doubtful, cf. Mertens ('93), Galeotti ('95), 

 Melissinos and Nicolaides ('90), Weismann and Ishikawa ('89), Ver Ecke ('93), 

 Steinhaus ('88), Henneguy ('93), Julin ('93b). 



2 For the central masses of chromatin found in many protozoan nuclei, Doflein 

 ('98) proposes the term " chromatosphere." 



