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 ovarj-- 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, do\\Ti 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 caljTc 

 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 

 300 



