No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 287 



a larger and a smaller sphere may be distinguished, which, 

 however, are not connected in any way whatever . . . but 

 perfectly free and independent of each other." 



Mark ('81) finds that during the maturation of the egg of 

 Limax campestris the male as well as the female pronucleus 

 may contain as many as fifty or sixty "pronucleoli," which dis- 

 appear before the copulation of the two pronuclei. In an 

 undetermined species of Lifuax he " observed in both female 

 and male pronuclei a single nucleolus of much greater size and 

 more deeply stained than the other nucleoli." 



Pfitzner ('81) finds that the " Kernsubstanz" is contained in 

 the reticulum and the nucleoli ; the latter lie within the meshes 

 of the former, and their role is problematical. " Wahrend des 

 weiteren Verlaufes der Karyokinese verschwinden sie, werden 

 anscheinend allmalig aufgezehrt, ohne direkt mit dem Geriist 

 in Verbindung getreten zu sein." 



Retzius ('81, cited by Van Bambeke, '85) : the nucleoli are 

 simple local accumulations of the chromatin, derived from the 

 nuclear reticulum. 



1882. 



Blochmann ('82) observed in the Qgg of Neritina one large 

 nucleolus containing a vacuole. Preceding the pole body pro- 

 duction, the nuclear membrane vanishes, and the nucleolus at 

 first retains its original size, then breaks up into several equal- 

 sized fragments. " Dass die Elemente der Kernplatte aus 

 Theilstiicken des Nucleolus entstehen, kann bei unserem 

 Objekt keinem Zweifel unterliegen, da ich alle Uebergangszu- 

 stande vom unversehrten Nucleolus bis zur ausgebildeten 

 Kernplatte beobachtet habe." After the two pole bodies have 

 divided off, the remaining chromosomes in the female pro- 

 nucleus fuse together to form a deeply staining, spherical 

 body, which resembles the original nucleolus. 



Flemming in his classical work ('82) gives the following defini- 

 tion of nucleoli: " Substanzportionen im Kern von besonderer 

 Beschaffenheit gegeniiber dem Geriist und dem Kernsaft, fast 

 immer vom starkeren Lichtbrechungsvermogen als beide, mit 



