| Figure 5.1 The Reproductive
Tract of Birds (A) A diagrammatic view of a hen’s oviduct. The ovary is surrounded by the infundibulum of the oviduct and ovulated eggs enter the oviduct via the infundibulum, where fertilization occurs. As the fertilized egg travels down through the magnum, isthmus, and uterus, the egg white proteins, the shell membrane, and the shell itself are successively added before laying. (B) The state of the blastodisc, shown in a longitudinal sections. The cleavage is called meroblastic because only the small disc of cytoplasm on one side of the yolk undergoes cell division. By the time the egg is laid, an anteroposterior axis has been established, the hypoblast is forming from the epiblast, and there are about 60,000 cells in the blastodisc. The portion of the blastodisc on the upper end (with respect to the earth’s surface) becomes posterior, the lower end anterior. A fluid-filled space below the blastoderm is called the subgerminal cavity. |
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Figure 5.1 |