What are-

1.ectoderm

2.mesoderm

3.endoderm ???

please explain briefly.

Ectoderm,mesoderm and endoderm are the three germ layers which are found during the development of embryos of animals including mammals.Each of these germ layers is destined to develop specific organs and organ systems of the individual to be developed.
1.Ectoderm-- It is the outermost layer of the embryo which differentiates to form structures like skin,brain,spinal cord and nerves.
2.Mesoderm--- It is the middle layer which differentiates to form structures like muscles,heart,blood vessels,kidneys,gonads etc.
3. Endoderm-- It is the innermost layer of the embryo which differentiates to form structures of digestive and respiratory system,urinary bladder and the middle part of the ear.

Ectoderm, mesoderm and endoderm are called germ layers which are responsible for the body organization in animals.

A germ layer is a primary layer of cells that form during embryogenesis. It differentiates into ectoderm, mesoderm and endoderm. Each germ layer is involved in the development of different organs.

1. Ectoderm is one of the three primary germ cell layers in the very early embryo. It emerges and originates from the outer layer of germ cells. the ectoderm differentiates to form the nervous system (spine, peripheral nerves and brain), tooth enamel and the epidermis (the outer part of integument). It also forms the lining of mouth, anus, nostrils, sweat glands, hair and nails.
2. Mesoderm is the middle layer present between the ectoderm and endoderm. The mesoderm forms connective tissue, mesothelium, non-epithelial blood cells and coelomocytes. Mesothelium lines coeloms; forms the muscles in a process known as myogenesis, septa (cross-wise partitions) and mesenteries (length-wise partitions); and forms part of the gonads (the rest being the gametes).
3. Endoderm is the innermost layer.[1] Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm. The endoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of multiple systems.