44C KING. [Vou XIX. 
tions through an embryo in this stage of development show 
that the anterior portion of each genital ridge has developed 
much more rapidly than the rest and that this region contains 
from five to eight large primordial germ-cells (Fig. 2), while 
the middle and posterior regions never contain more than 
three of these cells at this time. The anterior part of the 
genital ridge, which has begun to develop into Bidder’s organ, 
is continuous with the part which later becomes the sex-gland, 
and the cells in one region appear exactly like those in any 
other (Ci. Fig. 25 Plate Voand Pics, Plate 1), At ties 
ginning of its development, therefore, Bidder’s organ is com- 
posed of two kinds of cells: large rounded primordial germ- 
cells which have a faintly staining polymorphic nucleus; and 
small peritoneal cells in which the nucleus stains very deeply 
and is usually elongated. There are no intermediate stages 
between these two kinds of cells, and in Bidder’s organ, as 
in the sex-gland proper, the primordial germ-cells must arise 
from undifferentiated embryonic tissue. 
Bidder’s organ develops much more rapidly than the sex- 
gland, and it has attained a considerable size long before it 
is possible to ascertain the sex of the individual. During the 
very early stages in the development of Bidder’s organ the 
large germ-cells divide by mitosis; the stages in this process 
being similar to those taking place in the cells of the sex-gland. 
In the prophase of mitosis twenty-four deeply staining chro- 
matin segments are formed which condense into V-shaped 
chromosomes (Fig. 3, X). The spindle has a small centro- 
some at each pole which is devoid of radiation (Fig. 3, Y). 
It is only the early generations of germ-cells in Bidder’s 
organ that are able to divide by mitosis; in later development 
the division of the cells is invariably by amitosis. In a series 
of papers dealing with the germ-cells of Moniezia, Child (8, 
9g) has maintained that amitosis is the usual method by which 
the germ-cells in this form increase in number, and he is in- 
clined to believe that amitosis occurs much more frequently 
in normal development than most investigators admit. Ami- 
tosis is the normal method by which the germ-cells in Bidder’s 
