SEX STUDIES. XI 27 
sperm formed and others have no trace even of seminal tubules 
in their structure, 
VI. DISCUSSION 
The study of the anatomy and histology of this whole series 
of birds somewhat abnormal as to sex shows that they are all 
fundamentally female, except the guinea chickens. These 
are merely sterile males with consequent indifferent behavior. 
The hens with a tendency to tread other hens are normal active 
females. The eight other birds are fundamentally female, 
either undeveloped or degenerating. Every bird has in its 
embryonic development an undifferentiated sex stage as far 
as organs are concerned. It has the ducts for both sexes, and 
the gonad has the same early development regardless of whether 
it develops later into an ovary or testis. This undifferentiated 
gonad consists of a mass of sex cords growing out from the mes- 
onephros covered over by a thickened germinal epithelium. If 
the bird becomes a female, the left Millerian duct enlarges and 
the germinal epithelum proliferates and forms most of the 
reproductive organ. If the bird becomes a male, the Miillerian 
ducts degenerate, the Wolffian ducts become larger and coiled, 
and the sex cords become the main part of the reproductive 
organ. One of the Holland birds, 1429, is nearly a normal fe- 
male. Three of the Holland birds, 1428, 1425, 1427, are evi- 
dently undeveloped females. They have infantile oviducts 
and embryonic ovaries. The other four birds are also fun- 
damentally female, but show that the reproductive apparatus, 
has passed through a female stage and has become partly or 
largely male. In 1426, the ovary is partly embryonic, and part- 
ly degenerating, and a testis with active sperm has formed on 
the right side of the body. It has the oviduct of a laying hen. 
The other three: birds have large gonads on the left side only 
and in all three cases the ovarian portion shows signs of degen- 
eration and the testis portion signs of development. <A trans- 
formation such as this can be easily understood from the embry- 
onic development. The sex cords in the core of the gonad 
hypertrophy and form seminal tubules, while the oocytes and 
