334 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 Sida, into two periods, "von denen 

 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 lloina are as in Cyclops 

 (just described). In Sida 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) Lavicllibranchiate 

 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, Aiiodonta, 

 Cyclops brevicortiis) ; (2) Echinoderm type, with one large 

 " Hauptnucleolus," which increases in size, and only towards 

 the close of the " Keimblaschenstadium " do a few smaller 

 nucleoli appear {Toxopncustes, Sida crystallina, primiparous 

 Cyclops strenuus and C. signatus) ; (3) Vertebrate type, with 

 several nucleoli varying in size, number, and form {Raiia and 



