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[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 Inftisoria ; in con¬ 
nection with this view may be mentioned the observations of 
Butschli (’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 . 1 Some of the nucleoli of Protozoa 
are comparable to those of Metazoa , but it is doubtful whether 
all of them are . 2 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 “ nucleoles nucleiniens ” of Carnoy (’85), 
and the “ Karyosomata ” of Ogata (’83), Lukjanow (’87b), and 
Macallum (’ 91 ) are undoubtedly not nucleoli but portions of 
the nuclear reticulum. While the “ erythrophilic ” nucleoli 
of Auerbach, the “ Eunucleoli ” of Rosen, the “ nucleoles 
1 On the genetic relation of nucleoli to Balbianian 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.” 
