they were unable to lay eggs because the oviduct was ruptured 
at the isthmus. The ovary was normally developed and there was 
a normal growth and ovulation of yolks. However, as the yolks 
could not go through the oviduct, they passed into the abdominal 
cavity where they caused peritonitis. Ina male, having genetic 
factors for this atresia isthmi, there was curiously shown a 
rupture of the dextral seminal duct just posterior to the testis. 
This defect, which in females has a typical sub-lethal effect, 
is assumed to be caused by a single dominant factor. In males 
the defect does not have a lethal effect. If only one of the 
seminal ducts is ruptured, it follows that the defect can be 
passed on to progeny through the male. 
A somewhat similar condition has been described by 
Cole and Hutt (1953). These authors reported that of 324 non- 
layers, 8 per cent had incomplete oviducts. In most of these 
birds, the infundibulum portion of the oviduct persisted while 
a section from the magnum degenerated. In some cases the isthmus 
was also lacking. The ovary apparently functions normally and 
releases fully formed, normal ova, all of which are apparently 
resorbed soom after ovulation without having entered the oviduct. 
The birds appear normal in ovarian activity, in physiological 
changes in the external appearance of the body and in the in- 
ternal organs and as well as in behavior. The proportion of 
non=-layers in the population ranged from 0.3 to 2.9 per cent 
in four successive years. The authors believed that the differ- 
ences among strains and sires may indicate genetic factors 
involved. Sturkie (1955) performed laparatomies in hens that 
appeared to be in productive condition but which were not actue 
ally laying. In most birds, the ovaries and oviducts appeared 
normal, and there were no ova in the body cavity, suggesting 
that ova were resorbed. Egg yolks were introduced into the 
body. cavities of such birds and also of normal hens, and the 
incisions were closed. Twenty-four hours later, the birds were 
autopsied and inspected for the presence or absence of yolks. 
No trace of egg yolks was found in most of the birds indicating 
that yolks had been resorbed, 
Hutt et al (1956) described several conditions of 
nonelayers in a flock of 13,000 White Leghorn chickens in which 
he found a frequency of 1.58 per cent of nonelayers at 13 to 15 
months of age. The authors classified the different types of 
non-layers as follows: t1l--ovary inactive; 2--ovarian retrogression; 
5--ovulating non-layer; 4--oviduct discontinuous, cystic; 5-- 
oviduct inpacted; 6--abdominal inclusions; 7--other conditions 
(polycystic ovary, undeveloped oviduct, eystic right oviduct). 
The highest frequency was found to be ovulating non-layers, 
discontinuous or cystic oviducts and ovarian retrogression,. The 
frequency of ovulating non-layers was 4.4 per 1000. The authors 
found that most cystic oviducts are discontinuous, but that some 
are complete and closed at the anterior end. They indicated that 
the former type is probably congenital, though not necessarily gen- 
etic in origin, but that the latter can develop after laying 
has begun. The frequency of discontinuous oviducts was found to 
be 7.7 per 1000 pullets at 20 weeks of age. Mortality in these 
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