12 ALICE M. BORING AND RAYMOND PEARL 
We shall consider next the Holland birds, and begin with 
the most female of them. No. 1429 is shown in dissection in 
figure 10. This is a photograph of a part of the back of the 
bird with all viscera removed except the urogenital system. 
The posterior end can be distinguished by the small piece of 
rectum remaining where the digestive tract was cut off slightly 
above the cloaca. The ducts can be seen, all connecting with 
the cloaca, and extending anteriorly to the region of the repro- 
ductive organ which lies at the most anterior end of the dissec- 
tion. This one reproductive organ lies to the left and is an 
ovary with many oocytes visible to the naked eye, and a few 
very small orange spots like remnants of corpora lutea. The 
large round dark object to the left of the ovary is a tumor more 
than twice the size of the ovary. There is a normal oviduct 
with coils but the bird never laid an egg while in the Station 
flock. The two median ducts are the ureters. The right Wolf- 
fian duct shows its entire length plainly from cloaca to a spot 
opposite the ovary. It is somewhat coiled at the posterior 
end. At the anterior end, there is a slight enlargement, which 
proves in section to be a mass of tubules, resembling an epididy- 
mis. This is probably the remains of the mesonephric tubules, 
sometimes spoken of as a parovarium. A small portion of the 
left Wolffian duct shows in the photograph median to the ovi- 
duct. This is also somewhat coiled. There seems to be nothing 
male about the anatomy of this bird. It has an ovary and ovi- 
duct on the left and two Wolffian ducts. The only abnormal 
feature is the large tumor, which, of course, shows a diseased 
condition. The anatomy of the bird is, in short, that of a fe- 
male in the non-laying condition with a large tumor. The 
histological study of the ovary shows it to differ in some points 
from both the old Campine past the laying condition and the 
actively laying birds, described in studies [IX and X. In general 
it resembles the Campine more closely; that is, there is a large 
relative amount of stroma and there are no very small develop- 
ing oocytes (fig. 18). The oocytes present are of medium size 
and lie in normal follicles. In addition there are a number of 
cystic follicles filled with a watery fluid. These are visible to 
