10 ALICE M. BORING AND RAYMOND PEARL 
they are single straight tubes, sometimes they show the char- 
acteristic coils of a vas. Always toward the anterior end, and 
sometimes posteriorly also they have branches. These are 
probably remnants of the connection with the mesonephric 
tubules in the embryo. 
In the laying hens, it is sometimes hard to identify the Wolf- 
fian duct on the left side on account of the coils of the large 
oviduct. That it persists on the left as well as on the right 
side, however, is established beyond a doubt by the fact that it 
was found on some of the laying hens, and also by the fact that 
all seven of the young female chicks had two Wolffian ducts. 
We agree then with Goodale that the presence of Wolffian ducts 
in an adult bird is not necessarily a sign of maleness. 
V. ANATOMY AND HISTOLOGY OF ABNORMAL BIRDS 
The internal structure of this series of abnormal birds shows 
varying degrees of abnormality, and the interest of the study 
lies chiefly in seeing whether there is a close correspondence 
between these and the abnormalities of external structure and 
behavior. We have seen that the normal female has two Wolf- 
fian ducts of varying sizes, besides the left ovary and oviduct, 
so that the presence of Wolffian ducts is not a sign of maleness. 
No oviduct has, however, been found in any male, so its pres- 
sence may be considered a sign of femaleness of internal struc- 
ture. The external appearance of the reproductive organs has 
proved to be insufficient to distinguish between an ovary and 
a testis. An organ with a few projecting oocytes may be partly 
testis, and an organ without any visible oocytes may be ovary, 
testis or both. In deciding whether certain tissue is ovary or 
testis, the only indisputable criterion is when it has oocytes or 
spermatozoa. The general structure of the organ is, however, 
usually sufficient to show the difference in sex even when in 
an inactive condition, the testis being composed of tubules 
with a small quantity of connective tissue between them, and 
the ovary being largely stroma. However, there are some in- 
termediate conditions found when it is difficult to sex the organ 
as they both develop from a stage when the sex cords grow 
