CHAPTER XVIII. 
FORMATION OF THE EGG AND CHICKEN. 
THE reproductive organs of birds, and especially of the domestic 
fowl, are among the most complicated, since they must not only 
produce the ovum, but must enclose it in a protective envelope 
or sac, and supply nourishment for the embryo when growth sub- 
sequently takes place. As the ovum is developed after it is out- 
side of the body, this elaborate protection is necessary in order 
to preserve it in its original form, to retard evaporation of water, 
and at the same time to permit the absorption of oxygen and mois- 
ture. The reproductive organs are composed of the ovary and 
the oviduct (Fig. 145). The oviduct is divided into two distinct 
parts, one secreting albumin and the other the shell. 
The Ovary.—The active ovary lies on the left side of the body 
posteriorly, close to the backbone. It resembles closely a bunch 
of grapes which vary in size from that of a walnut, when the ovum 
is fully developed, down to that of a pin-point. The ovum corre- 
sponds to the yolk or yellow part of the egg. All hens have at 
maturity a certain number of embryonic ova, which represent all 
the eggs or yolks which it will be possible for them to develop dur- 
ing life, the rapidity with which these will mature depending upon 
management and feeding. The development of the ovum is 
brought about through an excess of feed, that is, material beyond 
what is required for maintenance and growth; hence egg production 
cannot attain its maximum unless plenty of feed be given. By 
the accumulation of yellow or yolk the ovum is brought to matur- 
ity, the yolk sac or calyx distends, and, as development progresses, 
the yolk sac becomes detached from the ovary and completely 
covers the ovum. When the ovum reaches maturity, the calyx 
or yolk sac gradually recedes along the white stigma line, allowing 
the egg or yolk proper to slip from the capsule, at which time it 
drops into the expanded, upturned opening of the oviduct. The 
remaining calyx immediately contracts, rapidly diminishes in size, 
and is soon entirely absorbed. 
The oviduct is a large tube, whitish in color, which starts from 
a point just below the ovary and ends at the cloaca. During the 
breeding season it becomes much enlarged, and is covered with a 
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