Describe different germ layers in animals.

Explanation

Germ layers. All multi-cellular animals develop from a single cell, the zygote which undergoes cleavages and produces a morula and then hollow ball of cells, the blastula. Afterward, the blastula changes into a two layered structure called gastrula. The outer layer of cells is called ectoderm, while the inner layer as endoderm. Later on a third layer, the mesoderm, develops between the ectoderm and endoderm. The three embryonic layers are called germ layers (germinal layers). They give rise to all organs of the adult. Ectoderm produces skin nervous system etc., endoderm produces the inner lining of the gut and digestive glands. The animals having three germinal layers are called triploblastic. In coelenterates and sponges the mesoderm is absent. Such animals are called diploblastic. Mesenchyme or mesogloea is present in diploblastic animals.