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 Limax 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 egg 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 
