No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 325 
does not become a “ Nebenkern ” (in opposition to the views 
of Ogata). In the eggs of Rana and Necturus the chromatin is 
“ principally collected in the form of nucleoli at the periphery,” 
but it is also contained in certain threads in the nucleus. He 
concludes from the study of the reactions of the substances 
to the indigo-carmine stain: “ the peripheral nucleoli generate 
a substance, therefore, which diffuses gradually through the 
nucleus, then into the cell protoplasm, the point in time of the 
latter occurrence corresponding with the formation of the yolk 
spherules. The mode of origin is through a process of deposi¬ 
tion from the nucleus of a substance allied to chromatin in the 
cytoplasm. ... I regard the yolk spherules as formed by the 
union of a derivative of the nuclear chromatin with a constituent 
of the cell protoplasm.” 
C. Schneider (’91) concludes that the true spherical nucleoli 
“ ebenso wie die Klumpen [of the chromatic network] aus 
[achromatischen] Gerlist und Chromatin bestehen und die 
Unterschiede beider nur morphologischer Natur sind.” In the 
testicle cells of Astacns the nucleoli are spherical, with “ eine 
deutliche Membran an und durch welche genau wie bei der 
Kernmembran [achromatische] Geriistfaden treten. . . . Der 
ganze Unterschied zwischen Nucleolus und Klumpen besteht 
also hier darin, dass um ersteren die Fasern zu einer Membran 
sich zusammenlegen . . . was man ringformig am Rande des 
Nucleolus wahrnimmt, ist sicher nicht die optische Wiedergabe 
einer Membran, sondern durch das Brechungsvermogen der 
Wandung des Nucleolus veranlasst.” The nucleolus in eggs of 
Echinodermata is homogeneous only in the final stages of its 
formation. Nucleoli are only metamorphosed portions of the 
true chromatin, and represent reserve masses of this substance : 
“ die Zusammenballung kann nur eine Befreiung der chroma- 
tischen Substanz von ihrer Arbeitsleistung bedeuten.” 
Wolters (’91) studied the sporulation of Monocystis: in the 
youngest individuals there is one nucleolus, which “ in seinem 
Innern sich starker tingirende chromatische Kugeln fiihrt.” In 
larger individuals the nucleolus consists of eight spheres, “ Diese 
Kugeln fiihren in ihrem Innern wieder Stabchen und Korner.” 
Just before the conjugation of two individuals this compound 
