No. 2.] THE OOGENESIS OF BUFO LENTIGINOSUS. 4II 
nemerteans the nucleoli are first found closely applied to the 
inner surface of the nuclear membrane. “It would seem that 
the yolk is at first present in the cytoplasm in the form of a 
diffused, unstainable fluid; that a portion of it, that remain- 
ing in the cell body, later becomes segregated as, or chemically 
changed into yolk globules; and that another portion of it 
is taken into the nucleus and, after passing the nuclear mem- 
brane, is changed into nucleolar substance.” Such an origin 
for the plasmosomes in the ova of Bufo seems unlikely since 
these bodies are not found close to the nuclear membrane until 
a late period in the development of the ova. 
The large nucleolar masses found in the oocyte at the stage 
of Figs. 26-34 correspond evidently to the “primary nucleoli” 
of Carnoy and Lebrun. I have shown that these bodies are 
complex structures composed of plasmosome material and of 
the chromatin which did not go into the formation of the 
chromosomes and that they later resolve into their constitu- 
ent parts; they are never formed entirely of chromatin, as 
Carnoy and Lebrun maintain. The fantastically shaped nucle- 
olar bodies found at the stage of Fig. 44 are similar in struc- 
ture to the large compound-nucleoli shown in Figs. 26-34, and 
they too resolve into chromatin threads and plasmosomes. In 
the egg of Bufo there is never any connection between the 
nucleoli and the chromosomes. Only oxychromatin goes into 
the formation of the compound-nucleoli, and the oxychromatin 
filaments which are formed by the resolution of these bodies do 
not at once disintegrate to form a new generation of nucleoli 
but they gradually break up into minute granules which seem 
to be absorbed by the achromatic substance of the nucleus. It 
is impossible to determine whether these granules take any 
part in the formation of the chromosomes which are found on 
the maturation spindle. 
VII. THE CHRoMOSOMES. 
At no period in the development of the odcyte does the basi- 
chromatin disappear nor does it become condensed in the form 
of nucleoli, and the chromosomes can be traced continuously 
