The main component of eggshell is calcium carbonate, and the key to its formation is calcium deposition. The basal layer of eggshell can only be formed by organic scaffolds composed of protein and mucopolysaccharide, and the eggshell can only be formed after calcium carbonate crystals condense and grow between scaffolds. Calcium deposition changes with time, and the speed is slow at first, and then it will gradually accelerate. As the egg stays in the uterus for 5~6 h, the calcium deposition will maintain a fairly consistent speed until the egg leaves the uterus.

2. Shell membrane

Shell membrane is a fiber membrane wrapped around protein, and it is an organic fiber net composed of tough keratin. The shell membrane is divided into two layers: the shell membrane is thick and close to the eggshell, which is an opaque and unstructured membrane, and its function is to prevent water from evaporating from the egg contents; The inner shell membrane is about 1/3 of the thickness of the former, and it is attached to the inner layer of the outer shell membrane, through which air can freely pass.

3. protein

Egg white has at least three layers, the outer layer and the inner layer are relatively thin, and the middle layer accounts for about 65% of the whole egg white. Because it contains about 0.3% fibrous mucin, it is sticky, while the inner and outer layers contain little such mucin.

4. Egg yolk

There is a layer of yolk membrane on the surface of egg yolk, which is the innermost protective structure in the internal structure of egg. Generally, yolk consists of yellow yolk and white yolk in concentric circles, with yolk heart in the middle. There is a small white disk (like a small white dot) on the yolk, which is composed of a part of cytoplasm and nucleus. When the egg is not fertilized, the blastoderm is light and small, and when the egg is fertilized, the blastoderm is slightly thicker. After fertilization, the blastoderm can hatch chickens under suitable conditions. The blastoderm, yolk membrane and yolk together form an egg cell.

5, blastoderm

A white spot on the surface of the yolk, the unfertilized egg is called a fertilized egg, and the fertilized egg further develops into an early blastoderm. The blastoderm of fertilized eggs is about 3 mm in diameter, and the ovule of unfertilized eggs is smaller and will develop into a chicken heart.

6. Egg yolk lacing

Egg yolk is generally layered, consisting of yellow yolk and white yolk alternately arranged in concentric circles, with the yolk center in the middle, the yolk center neck connected with the blastoderm, and thick protein at both ends of the yolk along the long axis of the egg, which keeps the egg in the protein center, plays a buffering role, prevents the egg from shaking, and is beneficial to the hatching of the egg.

7. Epidermal cuticle

The stratum corneum ('stratum corneum' in Latin) is the outermost layer of epidermis, which is mainly composed of 10 ~ 20 layers of flat dead cells without nucleus. When these cells fall off, the cells located in the basal layer will be pushed upward to form a new stratum corneum.

8. Yolk membrane

The yolk membrane is a part of the fertilized egg of birds, and it is a membrane attached to the surface of the egg. It belongs to the primary egg membrane, which is developed from the cell membrane of fertilized eggs and has protective effect. It forms in the ovary. It is generally believed that it is composed of secretions from follicular cells, and the egg itself may also participate in the formation of yolk membrane.

9. Egg shell

Eggshell is a hard or tough protective layer surrounded by eggs of oviparous animals, with small holes on it for gas exchange with the outside world. It is mainly composed of organic matter and calcium salt. It has the functions of preventing water evaporation and moisturizing, is the protective tissue of the outer layer, conducts light, heat and sound, and provides calcium needed for embryonic bone development.

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