Stages of a Baby Chicken Egg

Chickens develop rapidly from the single contributions of female and male chickens to a fully formed chick. Chick embryo development is similar to mammalian embryo development and is easily studied. Biologists often study chick embryos to understand the development of other species. Along with scientists, many backyard hobbyists are taking an interest in egg incubation for suburban chicken farming. A general knowledge of embryo development is helpful whether the eggs are incubating for scientific study, as a backyard hobby or for farming.

  1. Fertilization

    • A chicken embryo begins life in the same manner as most other species of animals. The hen's ovary releases an ovum, which is the female DNA contribution. The male's sperm makes contact with the ovum, but only one can enter the germinal disc to fertilize the ovum. According to Chickscope, the hen lays the fertilized egg around 24 hours after it is fertilized. Cell division begins within the first three hours. The cells group together on top of the egg yolk in a white spot.

    First Few Days of Incubation

    • Once the egg is laid, embryo development is interrupted when the temperature decreases to below 80 degrees Fahrenheit. As the egg's temperature increases through an incubator's heat or a nesting hen, cell development resumes. Mississippi State University asserts that the cells begin differentiating as the primitive streak develops. The head, eye and backbone begin developing along with the initial digestive track growth. The beginnings of the vascular system develop from blood islands that form on the first day of incubation. By the second day, those blood islands are linked together as the circulatory system forms. The heart begins beating before the close of the second day. On the third day some of the embryo's external features, such as the limb buds for the wings, begin to form.

    Days Four through Seven

    • The chicken embryo positions itself on the left side of the yolk. The body curls into a "C" position as the head and tail move closer together. The internal organs have all started their initial formation by the end of the fourth day. The digestive and respiratory systems continue to develop, creating nasal pits, a tongue and mouth. While development is well underway, the chick embryo still resembles any mammalian embryo.

    Days Seven through 21

    • Growth is rapid during this period of development. The thoracic cavity grows around the heart so that it is completely encased by the embryo body. Externally, digits form on the wings and feathers and feather tracts form and the beak hardens. According to Mississippi State University, claws develop on the 14th day. The embryo has a definite bird appearance now. On day 20 the embryo pierces the air cell and begins to breathe air. The embryo begins the hatching process on about the 21st day.