No. 2.] DEVELOPMENT OF BIDDER’S ORGAN. 447 
found in practically every section of Bidder’s organ taken 
from young toads or from adult males. 
By the time that the nucleus has reached the stage of Figs. 
10-13 the follicle cells have formed a membrane around each 
egg, the zona pellucida (Figs. 27, 28, 30). Not infrequently 
a blood corpuscle is to be found among the follicle cells which 
lie inside of the zona pellucida in contact with the outer sur- 
face of the cell (Fig. 19, B. C.). 
In the early stages of the development of Bidder’s organ 
the cytoplasm of the young oocytes contains a single vitelline 
body which is sometimes surrounded by a clear area as it is in 
the ovarian ova (Fig. 7, V). About the time of synizesis 
this vitelline body divides repeatedly, and by the time that 
the egg has attained a diameter of 0.035 mm. there are a num- 
ber of these bodies of various sizes scattered throughout the 
cytoplasm (Fig. 16). Will (33) and Leydig (20) maintain 
that the rounded bodies in the cytoplasm of the egg of Rana 
(which are similar to the vitelline bodies in the egg of Bufo) 
are nucleoli which have migrated from the nucleus into the 
cytoplasm in order to form the yolk. Such an origin for the 
vitelline bodies in the cells of Bidder’s organ is impossible, 
since these bodies are increasing in number at the time that 
the nucleus rarely contains more than three or four small 
nucleoli. As is the case in the ovarian ova, the vitelline bodies 
bring about the formation of granular yolk-nuclei in the cells 
of Bidder’s organ, and, at the stage of development shown 
in Fig. 19, the cytoplasm of the cells sometimes contains a 
large number of these structures. The arrangement of the 
yolk-nuclei in the cells of Bidder’s organ differs from that 
found in the ovarian ova, since these bodies are always scat- 
tered irregularly throughout the cytoplasm and are never 
collected in a zone midway between the nucleus and the per- 
iphery of the egg. In many cases the yolk-nuclei form in a 
very abnormal manner, and a cell, instead of containing a 
large number of small yolk-nuclei, will contain only two or 
three of these structures which are very large (Fig. 18). In 
such ova one of the large yolk-nuclei almost invariably forms 
