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MONTGOMERY. 
[Vol. XV. 
of the nuclei he concludes that the nucleolus divides (“nukleo- 
lare Kernhalbierung ”), since the nucleoli of the daughter-cells 
are of equal size. 
Hacker (’93a) divides the maturation stages of the ovarian 
eggs of Moina , Cyclops , and Si da, into two periods, “vondenen 
der erste gekennzeichnet ist durch die Anwesenheit eines 
einzigen ‘Nucleolus’ und durch die leichte Farbbarkeit des 
Fadenspirems (chromatische Stufe), der zweite durch die 
Anwesenheit mehrerer ‘ Nucleolen ’ und die Abneigung der 
chromatischen Substanz, die Mehrzahl der Farbungsmittel 
anzunehmen (achromatische Stufe).” In the first period 
(“ Wachstumsphase ”) there is one excentric, deeply staining 
nucleolus (“ Hauptnucleolus ”), which possesses a “ Hullmem- 
bran”; in the second period, in addition to the “Hauptnucle¬ 
olus” there are also one or two “ Nebennucleoli ” of greater 
size than the former, but staining less deeply, and somewhat 
irregular in form. Both kinds of nucleoli contain vacuoles. 
The “ Nebennucleolus . . . stellt sich vielfach als hohles 
Gebilde von ellipsoidischer Gestalt dar, dessen einem Pole der 
Hauptnucleolus kappenformig aufsitzt.” Only the outer shell 
of this nucleolus stains deeply. Subsequently the “ Haupt¬ 
nucleolus” grows gradually smaller and finally disappears; 
and at the same time the “Nebennucleolus” increases in size 
and becomes irregularly lobular in shape, and finally breaks 
into pieces. The nucleolar relations in Moina are as in Cyclops 
(just described). In Si da only a “ Hauptnucleolus ” is present, 
and this contains a large central and several smaller peripheral 
vacuoles. Hacker distinguishes the following types of ova 
with regard to their nucleolar structure : (i) Lamellibranchiate 
type , with one “ Hauptnucleolus ” and one or two “ Neben¬ 
nucleoli,” the latter larger and less chromatic than the former, 
but both frequently in close connection (Naja, Anodonta, 
Cyclops brevicornis ) ; ( 2 ) Echinoderni type , with one large 
“ Hauptnucleolus,” which increases in size, and only towards 
the close of the “ Keimblaschenstadium ” do a few smaller 
nucleoli appear (Toxopneustes, Sida crystallina , primiparous 
Cyclops strenuus and C. signatus ); ( 3 ) Vertebrate type , with 
several nucleoli varying in size, number, and form ( Rana and 
