*The embryo differentiates into germ layers. These germ layers are an outer layer ectoderm, inner layer endoderm and a middle layer of mesoderm that appears later in between ectoderm and endoderm. 

So, the correct answer is Ectoderm, mesoderm and endoderm'.

The primary germ layers in the development of an embryo are ectoderm, mesoderm, and endoderm. These three layers give rise to all the tissues and organs in the body.

Ectoderm:
- The ectoderm is the outermost layer of the embryo.
- It gives rise to the epidermis (outer layer of the skin), hair, nails, sweat glands, mammary glands, and the nervous system.
- It also forms the lens of the eye, enamel of teeth, and certain parts of the ear.

Mesoderm:
- The mesoderm is the middle layer of the embryo.
- It gives rise to the musculoskeletal system, including bones, muscles, and connective tissues.
- It also forms the cardiovascular system (heart and blood vessels), urogenital system (kidneys, gonads), and the dermis (inner layer of the skin).
- The mesoderm also gives rise to the lining of the body cavities (peritoneum, pleura) and the serous membranes.

Endoderm:
- The endoderm is the innermost layer of the embryo.
- It gives rise to the lining of the digestive tract, respiratory tract, and the glands associated with these systems.
- It forms the epithelial lining of the stomach, intestines, liver, pancreas, lungs, and thyroid gland.

Importance of Germ Layers:
- The development of these primary germ layers is essential for the formation of all the tissues and organs in the body.
- Each germ layer differentiates into specific cell types and tissues, contributing to the overall complexity and functionality of the organism.
- The ectoderm gives rise to the nervous system, which is responsible for coordinating and controlling bodily functions.
- The mesoderm forms the musculoskeletal system, which provides support, movement, and protection.
- The endoderm forms the lining of the digestive and respiratory systems, which are involved in nutrient absorption and gas exchange.

Conclusion:
In summary, the primary germ layers in embryonic development are ectoderm, mesoderm, and endoderm. These layers give rise to all the tissues and organs in the body, playing a crucial role in the formation and functionality of an organism.