THE OOGENESIS OF BUFO LENTIGINOSUS. 
HELEN DEAN KING. 
The present paper records the results of an investigation 
of the odgenesis of the American toad, Bufo lentiginosus, 
which was undertaken, primarily, in order to trace the history 
of the chromatin from the odgonia to the maturation period 
of the odcytes and thus to complete my study of the chro- 
matin behavior in the germ-cells of this amphibian. The 
work has necessarily involved a detailed study of the nucleoli, 
since these structures are closely associated with the chromatin 
at certain periods of development; and it has been extended 
to include an investigation of the yolk formation, as the 
material seemed especially favorable for this purpose. 
This study was begun several years ago at Bryn Mawr Col- 
lege, but was laid aside for various reasons until this past 
year, when it was completed at the Biological Laboratory of 
the University of Pennsylvania, where I was holding a Uni- 
versity Fellowship for Research in Zoology. I take this op- 
portunity to express my obligations to Professor E. G. Conk- 
lin for many valuable suggestions during the course of my 
investigations. 
I. MATERIAL AND METHODS. 
Bufo lentiginosus is found very abundantly in the vicinity 
of Philadelphia; and, as the tadpoles are easily reared in the 
laboratory, several different series of preparations have been 
obtained consisting of larve killed at frequent intervals from 
the time of hatching until metamorphosis. These series give 
all stages in the development of the germ-cells up to the 
early growth period of the odcyte. For the study of the later 
development of the ova, young toads with a body length of 
1.5-5.5 cm. were collected at various times from June until 
